This an old Equestrian joke:

Why did the sick pony visited the chicken coop?

Why?

Because the doctor said he needed a chicken soup!

....

I said it was an old joke not a good one.

But few ponies knew the story behind this particular joke.

*****

"As you can see, my dear Carrot Top; the origins of Equestria were actually pretty humble." the Doctor explained, waving a hoof at the small farms in front of them.

"A-ha." the earth pony answered, clearly uninterested.

The Doctor sighed. "You know, Derpy would have appreciated the opportunity to see this."

"Yeah, well yarh stuck with me partner." she retorted.

"Don´t remind me..."

"Hey look at that, an unicorn farmer. Well, ah be silly that ain´ something yah see everyday." she said, pointing at the nearest farm.

"Even better. Recognize his pony Cutie Mark?"

Carrot took a good look and once she saw the four-leaf clover, her eyes went wide.

"Precisely, he started as a simple peasant before Star Swirl recognized his true potential."

Now Carrot was genuinely impressed but soon the moment was interrupted by danger, something that happened a lot with the Doctor around.

"ARgh! That cockatrice is attacking the chickens!" Carrot said and rushed to help Clover.

It was a mess of feathers as the chickens ran away in fear, Clover unable to contain them. Carrot finally was able to trap the cockatrice in a bag and toss her away. Unfortunately not before it laid eyes on the Doctor.

"Doctor are yah...green?"

"Yes it seem I ACHU!" and a nearby egg hatched into a full chicken. "am."

"Ah don't understand. Ain´t yah supposed to turn intah stone when looking at a cockatrice?" she asked.

"Usually but Time Lord physiology is kind of tricky. Instead I seem to have come with a severe case of Chronic Flu, in this case Chronic standing for ACHU!" a small seed grew into a giant tree. "chronological."

"So yar gonna keep doing that?"

"And worse. If I don´t stop this I could be sick for over 50 years."

The mere idea made Carrot turn white. "Is there any cure?"

"Actually it is and its very simple too. I just need to drink a good hot bowl of chicken soup."

"CHicken soup?"

"That´s right."

"Ah ain´t gonna cook that!" Carrot yelled.

"Figures. This actually why I stop being a vegetarian, you never know when you gonna need a cure for a strange disease. Listen Carrot, I don´t actually need you to cook the poo chickens, just made a soup with their feathers and I´ll be just fine."

Carrot took a good look at the farm, all covered in feathers including the poor clueless farm.

"That might be a problem..."

****

The story of how Carrot recovered every single chicken will remain a mystery for eternity since the Doctor was unable to join her, instead staying on the farm watched by poor Clover, who had plenty of troubles understanding this weird ponies. It was at times like this that the Doctor miss his TARDIS and her handy universal translator.

Carrot finally returned at night, wearing a suit of armor for some reason; returning to a farm that was a complete mess of things that were too old or too young for their respective ages.

The Doctor took a good look at his companion as she entered the bedroom. "Should I ask..."

"Please don´t."

*****

The next morning the Doctor was perfectly fine and both he and Carrot leave, leaving Clover with plenty of questions that went unanswered.

Years later, CLover told the story to his mentor who repeated the story for the king who told his daughter who bragged about it with her friends who spread the gossip and somehow, centuries later the only thing ponies remembered were the words "chicken soup."