99 facing an odd bet

Villian is loose passive and has shown a tendency to call down when he hits the board.

Party Poker 2.00/4.00 Hold'em <font color="#0000FF">(10 handed)</font> link

Preflop: thejonesess is MP1 with 9[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/club.gif[/img].
UTG calls, <font color="#666666">1 folds</font>, <font color="#CC3333">Hero raises</font>, <font color="#666666">6 folds</font>, UTG calls.

Flop: (5.50 SB) 6[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG bets</font>

Now what?