[rando]

The passivity before the river suggests he could have A3 with something (wheel or good pair?). But man that river is a nuclear bomb. If I had to guess, villain either has A3 + higher card to pair the board or A4 and an overpair. But it's the prototypical spot where you try and bluff the other guy off the other end (i.e. A with a 3 or even a 4 and nothing else thinking your low is shot), and he's caught you with the prospects of making a call that can't feel at all good. I think my leaning here would be calling on the end, because I doubt he has A3 plus something that beats bottom two. Guessing you get quartered slightly less than half as often as you chop, with the freak scoop of something like KK34 with spades or some other wacky river semi-bluff attempting to steal something having just sat down.