I had literally just sat down so PT stats had not popped up yet (I'll put them in white at the end of the post). I was tempted to call this because it looked like a busted flush however with only $11 invested and in the absence of a read I decided folding was the best option. The A on the turn was a strange card, it is less likley he has the ace and really it probably just leaves the board the same, but most players would show some aggression when they hit their trips. Would potting the turn have been a better line? My $6 was really an attempt to block the move he ended up pulling on the river. If checked to me on the river I would probably have checked through

PokerStars No-Limit Hold'em, $0.50 BB (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

SB ($11)
BB ($39.05)
UTG ($48.70)
Hero ($48.75)
Button ($9)

Preflop: Hero is MP with K, K.
UTG calls $0.50, Hero raises to $2, 3 folds, UTG calls $1.50.

Flop: ($4.75) 3, A, 5 (2 players)
UTG checks, Hero bets $3, UTG calls $3.

Turn: ($10.75) A (2 players)
UTG checks, Hero bets $6, UTG calls $6.

River: ($22.75) 8 (2 players)
UTG bets $37.7 (All-In), Hero folds.

Final Pot: $60.45

Results in white below:
UTG doesn't show.
Outcome: UTG wins $60.45.

VP$IP 39 PFR% 6 Aggression factor 0.75 Hands played with 33 I felt a lot better in folding when I saw that aggression stat!