What does the joke that my ass hurts when I eat too much sugar mean?

This joke comes from a meaningful joke on the Internet:

The dog said to the kitten, guess how many sweets I have in my pocket?

The kitten said, you guessed it. Can you give it to me?

The dog nodded: well, I guess I'll give it to you two!

The kitten swallowed and said, I guess five dollars!

Then, the dog smiled and put the candy in the kitten's hand, saying, I still owe you three dollars.

This is not a joke with low IQ, but because I love you and I allow you a little greed.

The cat ate these two pieces of candy with a lot of sleeping pills excitedly and fainted.

The next day, the puppy took three pieces of candy to the kitten and said, I owed you three pieces yesterday.

The kitten said, no, my ass hurts when I eat too much sugar.

What it means here is that the candy that dogs give cats contains sleeping pills. After the cat fainted, it was forced to give the cat XOO, so the cat had a painful ass. The next day, the dog wanted to stay with the cat XOO, but the cat refused because it didn't know why its ass was too painful.