Kittens being fixed

Question
Hi Jana,
My male and female kittens went in to be fixed today. They were litter mates out of 5 kittens we found under my mothers house.  They have been best buds since they were born, but now when I brought them home, they are hissing at each other. The male is attacking his sister and hissing worse than she is.  What would be the reason for this and how do I get them to like each other again as they did this morning?

Answer
They both smell like an animal hospital to each other. Plus there is always mild discomfort after these surgeries so that is their warning to one another to leave each other alone for a day or so.
This is very common and always has resolved itself for the owners that have called us about it in the past.