Unknown SB leads small on the flop

[Mr. Curious]

$500 NL
Blinds are $5/10
9 Handed

SB is an unknown. I've only been at the table for two hands.

Stacks:
SB $350
Hero $500

Hero is dealt A[img]/images/graemlins/spade.gif[/img]Q[img]/images/graemlins/heart.gif[/img] in MP2

Preflop: UTG folds, UTG+1 folds, MP1 folds, Hero raises to $40, MP3 folds, CO folds, Button folds, SB calls, BB folds

Flop: Q[img]/images/graemlins/diamond.gif[/img]J[img]/images/graemlins/heart.gif[/img]2[img]/images/graemlins/diamond.gif[/img] (2 players)
Pot: $90

SB bets $25, Hero ... ?