Michael Phelps recently "raced" a shark, except Phelps didn't swim side-by-side with a real shark. He went up against a CGI shark ... that simulated how fast a shark would swim in a straight line.

Michael Phelps swam against a Great ... of sharks — but it was all simulated. Instead, Phelps raced against virtual versions of the sharks side-by-side based on their swim rate in a separate ...