Why is a giraffe's neck so long?
Because his head is so high up in the air.
Giraffe's Neck
Explanation
Explain Bear
Hey, listen up, slowpoke! The joke is that a giraffe's neck is long because its head is way up high. Like, duh! It's a silly way of stating the obvious, kinda like how you state the obvious when you ask for explanation of the joke.