NL50 KK Overpair against TAG

[dersl]

Full Tilt Poker, $0.25/$0.50 PL Hold'em Cash Game, 6 Players
LeggoPoker Hand History Converter

MP: $70.70
CO: $6.90
BTN: $88
Hero (SB): $57.10
BB: $101.65 15/12/2.7/19 (2k)
UTG: $54.95

CO posts $0.25
CO posts $0.50
Pre-Flop: K[img]/images/graemlins/club.gif[/img] K[img]/images/graemlins/heart.gif[/img] dealt to Hero (SB)
UTG calls $0.50, MP calls $0.50, CO checks, BTN folds, <font color="red">Hero raises to $3.25</font>, BB calls $2.75, 3 folds

Flop: ($8.25) 5[img]/images/graemlins/heart.gif[/img] 3[img]/images/graemlins/heart.gif[/img] 8[img]/images/graemlins/club.gif[/img] (2 Players)
<font color="red">Hero bets $6.25</font>, BB calls $6.25

Turn: ($20.75) 4[img]/images/graemlins/diamond.gif[/img] (2 Players)
<font color="red">Hero bets $13</font>, BB calls $13

River: ($46.75) 9[img]/images/graemlins/spade.gif[/img] (2 Players)
Hero checks, <font color="red">BB bets $22</font>, Hero ?


I'm not quite sure what kind of hands call on the flop and turn and bet the river. I think it's either some kind of slowplayed hand like a set or a total bluff from a busted fd. But his 50% potsize bets seems more like a valuebet that screams "call me"...