interesting live hand

[phifediggy]

7-handed, $5/10 blinds

i have around $1000 in the SB with A[img]/images/graemlins/diamond.gif[/img] 3[img]/images/graemlins/diamond.gif[/img]. 4 people limp, i complete, BB checks.

flop A[img]/images/graemlins/heart.gif[/img] K[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/heart.gif[/img]
i lead out for $40, BB calls fairly quickly, everyone else folds. BB has slightly less than i do, probably around $900 at the start of the hand.

turn 8[img]/images/graemlins/club.gif[/img]
i bet $100, BB thinks for a bit and calls.

river 8[img]/images/graemlins/spade.gif[/img]
i bet $175, BB goes into the tank and then raises to $400.

i had not seen BB do anything really tricky besides check-raising on a semi-bluff off the flop a few hands earlier. in general i'd say he was solid, though a few hands earlier i noticed his hand shake slightly when he had pocket jacks preflop. but now he sat still as i debated what to do.

thoughts?