Questions about the spam filter

Third-party mentions (you were tweeted by…) go to my spam filter. Askimet does this. However, yesterday two legitimate comments went to my spam filter as well. The first I can understand; it was a very long comment. The second? I have no idea why. I don’t see any settings in WordPress or Askimet that allow me to say “it’s okay to post a long comment.” And I would just like to know why those two comments went to spam.