Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Danny was visiting a museum.  He spent all day looking at exhibits.  He studied them all careful.  In the end, he went home.  Why might he have gone home?
tired feet
He was tired.