Trivia: There is no dialogue in the first 10 minutes of the film.
Trivia: When the camera crew were rigging the bridge to be blown up, the supervisor in charge of the detonation who didn't speak any foreign language thought he had been given the instruction to blow up the bridge and proceded to do it. Trouble was, the camera crew hadn't finished setting everything up and it was not filmed at all. Sergio Leone was (according to Clint Eastwood) the angriest anyone had ever seen him. As a result, the army agreed to rebuild the bridge for free and it hired a detonator who did speak the right language. This time they got the shot.
Trivia: Eli Wallach actually did get a black eye during his torture scene (but thankfully nothing more).
Chosen answer: Tuco knew he had a better chance at survival (and the gold) by playing along with Blondie and keeping his balance on the cross, hoping Blondie does not miss the rope when he shoots. This final, deadly game was preferable to being shot outright by Blondie and dying a poor man.
Scott215
Tuco had no idea that Blondie's intention was to shoot the rope and let him live.