I know it doesn't make much sense...but those of us who have been in Ponyville a while have learned over time that if Pinkie's a-twitching, you better listen. - Applejack
Alrighty. This episode. I've put it off for long enough. Let's go.
Spike and Twilight are working together on a spell to make Spike a tux, a cane and a top hat out of leaves, a stick and a rock. I'm not sure why they don't just ask Rarity to make the clothes for them. Maybe they're on a budget. Anyway, Spike is distracted at a critical juncture by Pinkie Pie being more Pinkie Pie than usual: running around with an umbrella hat on, and hiding under various places, like rocks.
Twilight asks Pinkie what she's up to and finds out that Pinkie's tail's a-twitching and that means stuff is going to start falling. Twilight laughs this off as ridiculous, and gets a frog to the face for her trouble... it falls out of the sky and lands on her snout. The frog came from Fluttershy and her autolevitating cart (Yet more proof of magical pegasus flight.) She's transporting them to Froggy Bottom Bog on account of the town pond getting too overpopulated. Bonus points for the poor guy who apparently is airsick.
Spike gushes in amazement about "Pinkie Sense", but Twilight is skeptical... even after falling into a ditch herself, right after Pinkie's tail twitches again. Applejack comes by and confirms that Pinkie Sense is real, even if it doesn't have a sensible explanation, having been proven multiple times to long-term residents of Ponyville.
Apart from twitchy-tail, Pinkie Sense can manifest as flopping ears, which means someone is about to get dirty - and a cart splashes Twilight with mud. While cleaning up, Pinkie continues to talk about her Pinkie sense... and we get an introduction to her pet toothless alligator Gummy (achy shoulder = alligator in the bathtub).
Twilight then tries to justify disbelieving Pinkie Sense on account of her experience that magic is something a pony chooses to happen, and takes effort and study... while Pinkie Sense makes no sense. Pinkie counters with a complete non sequitur about Pinkie Sense combinations... in which the order of actions is important. Earflop-Kneetwitch-Eyeflutter means "a beautiful rainbow", while Earflop-Eyeflutter-Kneetwitch means "Twilight gets a library door to the face courtesy of Spike" or in a non-vindictive universe, "watch out for opening doors".
Next Twilight tries to understand Pinkie Sense scientifically by hooking her up to a bunch of sensors, but Pinkie Sense is being coy and nothing happens. A frustrated Twilight throws a scientific hissy fit, and starts to walk out - only for a Pinkie Sense Combo to happen when Spike comes in looking for her, and flattens her with the door.
The next few scenes are a farce, with Twilight spying on Pinkie while trying to understand and/or disprove Pinkie Sense. The Vindictive Universe is in full effect here, making it a humiliation conga line for Twilight. She gets stung by bees, falls into AJ's apple cellar, and it culminates in a bunch of objects being dropped on her from a delivery truck ponied by Delivery Derpy (not a mailmare, exactly, but probably a nod towards the common Derpy fanon.)
AJ meets up with Pinkie and asks what she's doing. Pinkie brightly responds that she's busy letting Twilight spy on her without her knowing... only she does, but didn't want to spoil the secret. Twilight is not pleased...
Suddenly, Pinkie gets a new Pinkie Sense manifestation to add to her repertoire, an all over body shudder that predicts a doozey will happen at Froggy Bottom Bog... where Fluttershy was going. Worried that something bad might happen to Fluttershy, they charge off to the rescue, despite Twilight trying to be the voice of reason. She decides to tag along anyway, so she can gloat when they find out nothing's wrong.
Meanwhile, something is wrong... a monster appears to be stalking Fluttershy. However, when the others get there, she seems fine, prompting Twilight to be smug and announce that she knew Pinkie Sense was wrong... all while a four-headed Hydra rises up behind her. They manage to run away from the beast, but end up on a cliff with only a set of pillars to lead them to freedom. Fluttershy manages to get over with a hop, skip and jump, Spike follows, and Applejack drags the still-shuddering Pinkie over with her strength. Twilight buys time with a Leeroy Jenkins / Rainbow Dash move by charging the damn thing, managing to slip between it's legs, causing it to fall over on one of it's own heads.
However, despite this reprieve, the Hydra is still on her tail, and one of the heads crashes into the first few pillars, smashing them. Pinkie tells Twilight that she needs to take a leap of faith, and she does so... only to fall short. It looks like the end for Twilight... but a bubble from the swamp bounces her back into the air, and over to safety.
Twilight admits that Pinkie was right about the Hydra doozey, but suddenly Pinkie starts to shudder again... the Hydra wasn't the doozey. At this, it seems Twilight finally has cracked, as her mane and tail literally start flaming in rage. It's short-lived, and Twilight returns to normal, finally giving in and accepting Pinkie Sense, even if she can't explain it.
As it turns out, her believing WAS the doozey, and Pinkie trots off, happy that she has a new pawn for her soon-to-be-revealed plans to form a cult... or maybe, she's just being Pinkie.
In the final scene, Twilight asks Spike to take a letter, but he's distracted to see that Twilight is wearing an umbrella hat... because Pinkie's tail is a-twitching. After a hearty laugh, Twilight dictates her letter... sometimes, you find something unexplainable, but that doesn't mean it isn't real. You just have to have faith in it, and your friends. Spike opens a window to send the letter... and Celestia herself drops out of the sky onto the balcony to pick it up.
Thoughts on the Episode
Let's tackle that elephant in the room first, because that moral sure is a doozey. It's not quite a rejection of science for religion, since Pinkie Sense is a repeatable, observable phenomenon. That Pinkie Sense exists and works is perfectly clear, it's just that the mechanism is mysterious. In the same way, unicorn telekinesis works, but nowhere has there been an explanation of the mechanism responsible. It's just magic, and that is that. As for Twilight's contention that unicorn magic only happens when the unicorn chooses to do it...
We later find out from Rarity in "The Cutie Mark Chronicles" that it isn't even true. Filly!Rarity had no idea what her horn was doing, and even tried to fight against it. So Twilight doesn't know as much as she thinks she does. And she wasn't very scientific about it either.
Consider the scene where Pinkie's nose is itchy, and she seems afraid of something falling. Twilight says that's inconsistent. She doesn't consider the fact that there might be two distinct feelings that mean the same thing. Basically, she's already made up her mind that Pinkie Sense is not real, and is interpreting her observations in the light of that belief, thus not able to see all the possibilities.
The problem with the moral is that it seems to be saying, "If you don't understand the mechanism behind what you are observing, just give up and accept it." Needless to say, that attitude is not helpful for a true scientist. You should keep trying to understand the mechanism, even if you never manage to figure it out. Mystery is not to be valued if you are a scientist.
I guess all it really means is that Twilight is not really a scientist, and that's fine. Science is a wonderful way of exploring the world, but there are also other ways, and far be it from me to disparage others for their way of life. (Well, twice in one week, at any rate ) Also a quick note about the way Twilight seems to be punished by the universe for trying to find out why Pinkie Sense works. That's not a great moral either.
Enough about that. Let's talk about the Hydra. It's a little unusual to see one with only four heads, and of course, we never see one of them cut off, so the "two grow back" thing may not apply here. Our Hydras are different, perhaps? Or it may be that four heads was the point after which it got too hard to animate. At any rate, despite the fact that it tried to eat the ponies and Spike, the Hydra himself seems rather endearing (as endearing as a giant four-headed lizard-monster can be) One of the heads seems just a little bit slow on the uptake, although he did get a laugh out of the other heads smacking into things. He (the whole Hydra) even blows the ponies a raspberry as he leaves.
The small touches in this episode are great, like the aforementioned airsick frog, Pinkie rolling in the grass like a real horse, Twilight scooping up a running Spike to put him on her back. Of course, there are some small errors. After Pinkie starts shuddering, Applejack's barrel of apples vanishes, and reappears a few frames later; one of the Hydra heads rises up behind Spike and the rest of the group, but later all four are behind Twilight, things like that.
And of course, the fact that Twilight should just have been able to teleport over the chasm is ignored for the sake of drama. Oh well. Makes for a more exciting climax, I guess.
After the frog has crawled onto Twilight's cheek
Pinkie: "Um, Twilight... you got a little something on your face there."
Twilight: "Oh, really? Did your 'Pinkie Sense' tell you that too?"
Pinkie: "Nah, I could just see it... Lalala!"
Twilight leans on a barn door to show Spike not to be afraid of doors, but the door she should have been watching out for is the one leading to Applejack's new apple cellar.
Applejack (off screen): "Twilight! You came to visit my new apple cellar! How nice... Twi? You okay?... Uh, Twi...?"
This exchange on the cliff:
Spike: Do you know any spells for turning a Hydra into a mouse?
Spike: How about a squirrel?
Spike: How about...
Twilight: No small rodents of any kind!
Spike: That's too bad.
Rapidash Twilight. That is all.
Pros: Small touches. Introduction of Gummy. Some good comedy. A rather intimidating yet somehow endearing monster.
Cons: Possibly a questionable moral. Little animation errors. Twilight conveniently forgetting she can just teleport.
5 – Celestia Rank: A great episode. It will be re-watched frequently.
4 – Luna Rank: A good episode, but with one or two problems that prevent it from being great.
3 – Spike Rank: An average episode. Positives and negatives are balanced.
2 – Discord Rank: Worth watching once. After that, turn it to stone and put it in the garden.
1 – Nightmare Moon Rank: Send it to the moon!
Stay sunny side up!