Question: cats are hissing at each other?
Answer: Again, some hissing when they see each other is normal so don't be alarmed. Some light swatting is also common. Separate them if the hissing doesn't die down after 1 or 2 minutes or if there is any sign of threat (swatting with force, chasing, screaming, ears flattened, etc.). Try again when the cats seem to be calm.