Some of you already know this part. I have a 10+ years old female
(Kiki). About two years ago, I took an ailing young male off of the
street (Kitty). At first, Kiki attacked him frequently. Kiki has
learned to ignore him. Unfortunately, Kiki has been unable to cope
with his presence, perhaps partly because she is getting old. She
began throwing up every day. She also became aloof, she would
retreat to a loft up near the ceiling. Even when she would lie
between my chest and left arm (like she used to do frequently) while
I use the computer lying down, as she began to fall asleep she had
occasional violent spasms, her head would jerk as if waking from a
nightmare.

Not knowing the problem was anxiety, I had tried gradually switching
to different foods over many months. Something had to be done. I
tried separating Kitty from Kiki. The separation appeared to work
the first time for about one week. Then they weren't separated for a
while and Kiki started showing the same symptoms again. So again I
separated them for probably at least 12 hours every day. That has
been the case for over one month and Kiki is doing marvelously. I
had no idea Kitty would cause Kiki so much anxiety, but I'm relieved
to have found a workaround. The current situation is much better
than watching Kiki fall apart.

By the way. Kitty looks healthy and happy. I stopped trying to use
flea collars (they caused skin irritations and maybe caused Kiki a
wheezing lung problem) and bought a 4 month supply of Advantage. The
first application was a learning experience.

Have fun.