Why do chickens sit on eggs?

Tourist: Whose skeleton is that?
Sardar: An old king`s skeleton.
Tourist: Who`s that smaller skeleton next to it?
Sardar: That was same king`s skeleton when he was a child.

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Boy: why can’t bicycle stand up on their own
Girl: They are two tired.

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Cow1: why do chickens sit on eggs?
Cow2: Because they don’t have chairs.