My son walked in on my wife?

It seems to me that your son is attracted to his step mom. It's not exactly weird; some people don't consider their step-relatives actual relatives just because they aren't blood. The ten-second stare might have been from shock. If your son is that young, he probably hasn't seen anything from any of his girlfriends, so this must have been a light going off. He might be attracted to her, and it's not surprising. Granted, it's not really acceptable now considering that she's your wife and you're the only one that should be looking at her. Even it was all right in the USA perspective that step-relaitives could look at each other and feel no guilt, your son needs to back off because the woman is yours, not anybody else's. It may be a little awkward between the two of you if you confront him about it. He'll most likely deny any feelings about his step mom because he doesn't want to be called some kind of freak. You should tell your wife, though, about the keyhole incident. It's for her own good and peace of mind that you didn't tell her, but maybe if you and her talked about it, she might be able to talk to your son. If you say anything, it might end like a man-to-man challenge for the trophy wife. I hope what I put as an answer helps you.