[kurto]

Why call 1/5 of your stack with nothing? He could be bluffing you with a pair of 2s and beat you. A weak 8, 10 or J.

by the way- I tend to read his flop bet 1 of 3 ways-
"I have the draw and want to build the pot in case it hits"
"I have a small weak piece of it and want to let everyone know... but I don't feel that great about it so, if you reraise me, I'll probably fold."
or "I have a monster and hope I can induce a raise by betting weak."

If its 1 or 2, you're better off acting on the flop because you've shown weakness now and you've lost bluffing credibility.

If its 3... he's been trapping you and is looking to get paid off on the river.

Of all the options above... the weak "I'm on a draw bet" is the only one you're beating... though even then, someone drawing to a flush with K4... just hit big.

I fold.