Resident Cat (RC) sniffed NC’s pet bed and hissed.
Took a brush and collected fur from both cats. NC smelled RC’s fur and licked it; RC sniffed NC’s fur and (after a while) hissed.
When RC smells NC’s fur, it’s as if a reflex action kicks in and she involuntarily hisses.
RC heard NC meowing behind the master bathroom door; RC stopped, cautiously walked up to the door, sniffed, hissed, and walked away.
Later in the day, we let NC out of the bathroom to explore the master bedroom; during this time, RC hung out on the other side of the closed master bedroom door.
We noticed RC isn’t eating as much food as she usually does.
RC has lightened up, is eating, and seemingly back to her playful self. NC is getting tired of being confined to the master bathroom.
RC is uncharacteristically skittish with visitors in the house; NC is restless.
NC is sneezing and there is a discharge from her eyes. We contacted the veterinarian.
Took NC to the vet; she was diagnosed with an upper respiratory infection (and prescribed medication), so we had to keep her from RC until she got better. NC is confined to the master bathroom, but occasionally let into the master bedroom.