Yeah, that Alien is totally scoping out the guys ass. Apart from that, it's good. Change the pose of the alien (maybe creeping towards him?) and you've got a great pic.
One nitpick... I would have liked to see the alien in a more "I am going to kick your a$$" pose. He looks more like he is going to hug the guy. The dudes pose is good... very "WHat the hell was that noise" pose.