[GLKST526]

Yeah, that sucks, I can't imagine what you'd beat here other then a complete a total bluff. Looks to me like an A3 or something like that that backed into the straight, and he's worried that you aren't going to bet the river for him to check raise with 23457 on the board. I'd probably fold, or spite call to see if my read of ace and a pair on the board is right and then be angry when I lost, but I wouldn't recommend that particular course of action