re-introducing cats

Question
Hello Norman,
I have two male cats, both 3 1/2 years old, who have been pretty good friends for over 2 years. One of my cats got sick the other day and I took him to the vet. When we returned a couple of hours later, my other cat acted like he didn't know my sick cat. He growled, hissed and tried to attack him, like he was a stranger. What could have happened? Is it a scent from the hospital, another animal scent or a medication? Please help, the harmony of our household has been disrupted. Thanks

Answer
Rick,

This is not uncommon.  Cats know each other by scent, so you have hit the nail on the head. The scent of the hospital is overriding the normal scent. Usually within a few days to a week, things settle down and get back to normal.

Please let me know if this is, indeed, what happens.

Best regards.... Norm.