i'm not nearly as certain as you seem to be that BU doesn't have an A. would he really bet something like AsTs 100% of the time, especially if he also has inclination to believe SB is a nit. i'd like it if both players had checked twice, but i think BU's gonna show up with an A here a lot.

btw, preflop might be a vomit/fold. anyone else have thoughts on this?

EDIT: I PHAIL! didn't notice BU's bet sizing and the fact that CO is left to act. i'd flat, but i'm pretty much set mining here.