I only microwave the food for 9 seconds.  The cats seem satisfied with that.
A previous poster was microwaving much longer than that.

--
Barb
Of course I don't look busy,
I did it right the first time.

Good point, I should check my own mw for this possibility.

Another thing to check is if the food has gotten too hot to the touch.

For me, letting the food out for 1-2 hours to warm to the room temp is
more successful than other ways of heating, but she can still tell it
is not fresh.

This is the most surprising part. I open a fresh can and she eats 1/2
of it very happily. Close with a tight lid, refrigerate it, and 10-12
hours later warm it by leaving it out in the room, and now she is
reluctant to eat it.

I found re-heating to be a bit bad. Probably changes the fats, cooks
them.
I did find leaving the food out if not a favorite tends to eventually
work. The food warms up. If hungry enough, gets eaten eventually, even
re-heated food. I feel a little uncomfortable if leaving the food out
many hours, like 6+, but so far nothing bad happens. There are probably
different foods that are canned or wet that can be left out safely and
others that cannot be. We'll see. I guess the best is just a fresh can
and throw away the rest but that's a little expensive. I suspect
chicken may spoil less than the fish. I wonder if a cat is somewhat
resistant to some foods left out. The manufacturers all say NO-NO. One
said the tuna gets red because of bacteria after one hour but I have
not seen this with Fancy Feast. I eat food left out for many hours and
generally I can't remember any problems. In fact, the food if it ages
sometimes tastes much better, the flavors blend better and become more
distanct and tasty.