NL10 AK in CO facing strange flop donk.

[CaptVimes]

First orbit at the table. Never played with villain in hand before and he hadn't done anything remarkable in the few hands before this. I believe I had folded everything up until this point.


Full Tilt Poker - No Limit Hold'em Cash Game - $0.05/$0.10 Blinds - 9 Players - (LegoPoker Hand History Converter)

SB: $4.80
BB: $3.40
UTG: $12.90
UTG+1: $6.55
MP1: $9.35
MP2: $1.90
MP3: $11.00
Hero (CO): $9.85
BTN: $10.65

Preflop: Hero is dealt A[img]/images/graemlins/diamond.gif[/img] K[img]/images/graemlins/diamond.gif[/img] (9 Players)
UTG calls $0.10, UTG+1 calls $0.10, 3 folds, <font color="red">Hero raises to $0.50</font>, 3 folds, UTG calls $0.40, UTG+1 calls $0.40

Flop: ($1.65) K[img]/images/graemlins/club.gif[/img] 5[img]/images/graemlins/spade.gif[/img] 5[img]/images/graemlins/club.gif[/img] (3 Players)
<font color="red">UTG bets $3.40</font>, UTG+1 folds, Hero?