1. He's your boss, so even if he were overtly coming on to you and you were sure you were OK with that and wanted to reciprocate it still wouldn't really be OK because messing around with / fucking your boss is a really fucking bad idea.
2. It's sounds like you are a little curious so my best guess in this situation is that he isn't coming on to you at all, you just happen to be noticing these little things that he doesn't even realise he is doing.
Advice - ignore it. Say nothing, do nothing. Enjoy the show if you like looking at him but no more.