[AllIn3High]

How do you interpret his $40 bet? Is this AcA / KK / JJ looking for action or is it AQo hoping to steal?

Anyway, raising is terrible here, if he pushes you have to call and race for all your chips (or be crushed when he has a set). If he just calls your raise you're playing a $500 pot w/ $300 behind and have to push a blank turn w/o an advantage.

Folding is ofcourse out of the question.

.....Which leaves - calling, he's giving you a great price, and if his $40 bet really meant weakness you can pick up the pot on the turn by firering a half pot bet.