Bxe6, followed by hxg6
Shh, Quiet Bobby, an absolute KILLER move !
Qh6 with Qxh7 is almost mate, so yeah, Bg2 makes sense (because then it would be mate).
In a real game after noticing 2.Qxh7 wasn't mate, I would probably play 1.Qh6 anyway but with 2.gxh to win some material. But after reading mjgiordano's comment that seems right.

29.Bg2 - one of the Deadliest Quiet moves in chess history - but a Killer ! Play continued 29...dxc2 Black would have been confident he had the win here 30.Qh6 threatening mate Qf8 stopping it 31.Qxh7+!! sacing the Queen Black resigns 1-0. After 31... Kxh7 32.hxg6 double check Kxg6 then 33.Be4 mate. That's why Fischer played 29.Bg2 so he could manoeuvre it to the mating square e4 4 moves later !
It is Fischer to play White's 29th move. Does he try to press his attack, which looks threatening, but Black has the defensive ...Qf8 and the Ra7 is ready to cover the 7th rank ?
Or does he try and halt Black's foray, since after ...dxc2 Black will be threatening to Queen, not one, but two pawns, with other pieces bearing down ?
What did Fischer play in this position that his opponent probably gave little thought to ?
Try and solve it without looking
up the actual game.