brothers hissing

Question
A couple of days ago one of my cats who are brothers got out and was left outside for a night. when we found him in the morning his brother started hissing at him and batting his paw at him. Is this because he might have a different scent on him, and if so when does it stop.

Answer
Mike,

Your assessment is right on.  Yes, cats do know each other by scent and, after being outside, the one brother did have a different scent on him.  We also see this phenomenon after a cat has veterinary surgery.  Usually, after a few days to a week, things get back to normal as the outside scent wears off and the inside scent is re-established.

Best regards... Norm.