That is a very interesting fold. What do you think he had? He didn't have 44 or 77, and if he is playing a 4 or a 7 with a raise, he is playing very loose and give him credit for hitting a beautiful flop. Also, if he hit a full boat, wouldn't he try to extract a little more from you. He knows that you couldn't have him beat, so wouldn't he bet for value? To add to this point, he moved in after you CHECKED! He knew that your play was weak. If he had a real hand, he would definately not go in like that (unless he is thinking "maybe he'll think I'm trying to buy it"). Even with AA, I think he would try to extract a little more from you. My guess is that he put you on AK or AQ and thought you didn't hit.

He could have anything from 55 to QQ in my opinion, or nothing at all and sensed that your check was weak. I think this is a definate call.