I think they sometimes worry about other non-existent cats in the house lol

[luvmy2cats]

It's weird but I think sometimes that Sissy and Hootie aren't always aware of one another. I've noticed at times they seem startled by each others presence and have to sniff and check each other out. And sometimes if one hears the other eating or using the litter box they have to go investigate like there is going to be some strange cat eating their food or using their litter box.

 

[di and bob]

LOL! My cats do the same thing, I think they may be a little nervous, like they saw a strange cat out in the yard and think it may have come inside! They will even arch their backs, then relax and go sniff one another. Who knows, but they have to be unsure about something to act that way. I'm sure it's all perfectly normal, but be careful too, I've had my two actually attack each other and get hurt because of redirected aggression about something outside, so be careful!

 

[allenkm]

My boys act like this too, often after a visit from their "cousin" (the neighbor's cat who visits me from time to time) they will hiss at each other, then sniff, then lick each other. It's almost like they are saying oh sorry it's you.

 

[luvmy2cats]

 
LOL! My cats do the same thing, I think they may be a little nervous, like they saw a strange cat out in the yard and think it may have come inside! They will even arch their backs, then relax and go sniff one another. Who knows, but they have to be unsure about something to act that way. I'm sure it's all perfectly normal, but be careful too, I've had my two actually attack each other and get hurt because of redirected aggression about something outside, so be careful!

Once  I think Hootie was watching a stray cat through the window and then she went into the kitchen. Sissy came up behind her and she must have thought Sissy was the stray because she freaked and darted through the space between the dishwasher and cabinet. When I was trying to coax her out I notice there was a dribble of urine on the kitchen floor. So yeah I see your point about fights due to redirected aggression. I've also noticed that they hang out and sniff around the register vent in the living room. We live in a mobile home and I know strays hole up under the trailer so I have a feeling my girls can smell the strays.