False pregnancy?

Has anyone ever had a cat go through a false pregnancy before? What were the symptoms? I'm wondering because 4 and a half weeks ago, my cat Muffy was in heat and escaped for a few hours. She hasn't been in heat since. When I found her, she was hanging out with the neighbor's cat, a neutered male cat. Can neutered male cats still "perform" without making the female pregnant? (I haven't noticed any toms in the area.) I was reading a few books today, and it seems that maybe Muffy is having a false pregnancy. Although she hasn't gone back into heat, her nipples are not that pink and only stick out a little. Of course, I hadn't ever looked at her nipples before, so I'm not sure what they looked like before this happened. Anyway, I was just wondering if any of you have ever dealt with this type of situation before. Any comments?

Dawn

I have never had to deal with this, but in answer to the can male cats perform, yes they can but all it would do is throw her out of the heat cycle. She could not be pregnant through that one. However, it only takes a few seconds to become pregnant and she could have run into a tom that was intact. If it is a false prengnancy, the only way to tell is to take her into the vet about 28 days after she got out. The vet should be able to feel a fetus by then.