I have a 5 year old Maine Coon male and a 5 year old short hair calico female, both neutered both indoor cats. If I forget though and go out without shutting the door and get caught up in a conversation with a neighbor, the male will step out onto the porch.
If he is out for a minute or two, the female spits, snarls and claws him when he comes back in. The longer he is out the longer it takes for the strange smells he carries to disappear and for her to calm down.
Once he was out for up to an hour and it took her 4 days to accept him back.
I think it is the strange smells that the female (in our case) cannot understand and it makes him a foreigner to her.
