If a guy keeps checking you out everytime you're not looking whats going through his mind?

Specifically my ass. I do have a small waist & big ass which seems to garner attention.
Anyways met this guy through work and when I was walking away and he was in the car he stopped just to check me out when I looked back he looked away when he was behind me once I caught him looking and his eyes were dilated. When I walk away he will literally stand there staring at me and when I looked back he looked away again. Anyways there's been a few more times

What's going through his mind?
If a guy keeps checking you out everytime you're not looking whats going through his mind?
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