"pianists Martha Argerich and Nelson Freire have been playing together, or almost together, for many years. And more than most two-piano teams, they play for excitement.
That is risky business in a stage setup with pianos facing head-on, which doesn't allow the players to see each other's hands or, for that matter, much of each other at all. Some teams have devised gimmicks - heavy breathing, say, or facial twitches - to communicate; others play for safety and comfort."
It's all here