On the way back from Fluttershy's cottage, Twilight almost didn't register the familiar voice coming from a dead-end street on the outskirts of Ponyville.   "Twenty-one, twenty-one, twenty-one...."

She had a familiar sense of foreboding.  She knew that she should continue walking and not stop to find out what Pinkie Pie was doing.  Also, that she would stop anyway.

Twilight walked down the street towards the sound, until she saw a familiar pink pony, still chanting, jumping high up into the air and then landing on a ponyhole cover in the middle of the street, over and over again.  A crowbar was slotted into place just under the lip of the cover, as if she had been about to remove it and then gotten distracted by a sudden fit of jumping.

"Pinkie Pie?" Twilight asked.  "What are you doing?"

Pinkie landed on the ponyhole cover.  She cocked her head at Twilight.  She looked down at the iron cover.  She looked back at Twilight.

"Is this a trick question?" she asked.

Twilight shook her head violently, trying to clear it of the impression that Pinkie was making more sense than she was.  "Okay," she said, "I can see that you're jumping up and down on a ponyhole cover and shouting 'twenty-one!'"

Pinky nodded eagerly and gave Twilight a wide, congratulatory smile.  "You got it!"  She began jumping again.  "Twenty-one, twenty-one, twenty-one—"

"But why are you jumping up and down on a ponyhole cover and shouting 'twenty-one!'?" Twilight shoulded up at her.

Pinky came to a stop again.  She raised one hoof to her chin, perplexed.  "I don't think I understand the question."

"What's not to understand?  Why—"

"Stop!  That's it.  That word.  It confuses me."

"Why—"

"Yes!  That's the one."

"No, I mean—"  Twilight scrunched up her nose in thought.  "Why does it rain?"

"That's easy!" Pinkie said.  "Because pegasus ponies make it rain!  Didn't you know that, Twilight?  Twenty-one, twenty-one, twenty-one—"

"Of course I knew that!  My point was that you understood the question.  The use of the word 'why' indicates I am asking what caused some event."

"Yes," Pinky said, between jumps, "I.  Know.  That."  She came to a stop again and leaned forward to come nose-to-nose with Twilight.  "But since I am a sentient and purposeful agent, my will constitutes the final cause of all my actions, and your asking me for a cause of my jumping up and down when you can clearly see its final cause constitutes a violation of the Gricean conversational maxims, silly!"  She began jumping again.  "Twenty-one, twenty-one, twenty-one—"

"Gaaaaah!" Twilight said.  "How do you even know about Aristrotle and Grice?"

"Who?  Twenty-one, twenty-one, twenty-one—"

"Gaaah-aah-aah!" Twilight said, hoping to drive the point home this time.

She began pacing back and forth, while Pinkie kept jumping and shouting "twenty-one" at the pinnacle of each leap.  Phrasing her question, Twilight realized, was a semantic problem.  Pinkie literally did not know why she did what she did.  But Twilight was still curious; and that proved that "why," at least in the sense of intentions, wasn't what she really wanted to know.

"Twenty-one, twenty-one, twenty-one...."

Pinkie Pie's lack of conscious insight into her motivation wasn't mere cluelessness, Twilight realized.  Most people in fact had no conscious insight into any of their motivations; they merely invented them after the fact, as demonstrated by experiments in which people were asked to justify decisions that were the opposite of the ones they had actually made.  Pinkie was actually more self-aware than most in apprehending her lack of self-awareness.

"Twenty-one, twenty-one, twenty-one...."

Perhaps, Twilight thought, she should take a behaviorist approach.  She was interested in the operational effects of this activity, not Pinkie Pie's motivations.  And yet, she could not treat Pinkie Pie as a black box, as B.F. Skinhorse would have advocated, since the primary effects were probably some subjective emotional payoff.

But, if she focused on the action's conscious effects, rather than its conscious causes....

"Pinkie!" Twilight finally said.

Pinkie stopped.  "Yes?"

"How do you feel when you jump up in the air on a ponyhole cover and shout 'twenty-one'?"

"I feel great!"

"Hmm," Twilight said.  "Not really helpful.  Wait—hold on, give me a moment."  She smiled slyly.  "I've got it.  Pinkie, how would I feel if I jumped up and down on a ponyhole cover and shouted 'twenty-one'?"

"Well, that's a silly question!" Pinkie said with a laugh.

"GAA—Why is it any sillier than jumping up and down and shouting 'twenty-one'?"

"Because," Pinkie anwered, "the only way to answer it is to do it!"

"You're ... right," Twilight said.  "You're actually right."  Twilight shook her head again, even more violently.

"Course I am!  Twenty-one, twenty-one, twenty-one—"

"Pinkie ... Pinkie!"

Pinkie came to a stop yet again, smiling as excitedly as if she were just seeing Twilight for the first time.  "Yes, Twilight?"

"Pinkie, may I jump on your ... um ... can I try that?"

"Okie-dokie-lokie!"  Pinkie stepped aside, and Twilight stepped on to the heavy iron cover.  She looked up and down the street to make sure no ponies were in sight.

"Well," she said, "here goes."

Twilight began hopping up and down.

"You've got to count!" Pinkie said.

"Twenty-one.... twenty-one.... "

"Louder!"

"Twenty-one.... twenty-one...."

"Faster!"

"Twenty-one, twenty-one, twenty-one—"

"Higher!"

Twilight grunted as she jumped as high as she could, and shouted, "Twenty-ONE!  Twenty-ONE—"

At the top of Twilight's jump, Pinkie stomped on the crowbar with all four hooves.  The ponyhole cover flipped off like a tiddlywink, and Pinkie watched as Twilight dropped into the hole with barely enough time to register a look of surprise before she disappeared from sight.  A loud and disturbing thud came out of the hole.

Pinkie walked over to the cover, and kicked it until it slid back into place over the hole.  Then she walked onto it, and began jumping up and down again.

"Twenty-two, twenty-two, twenty-two...."