TL;DW: Mario blinks at a set interval even after level loads to prove legendary Japanese speedrunner of old, who even had a timing sequence named after him, of cheating by splicing. Even in the run that gave him his fame.
Quite interesting video showing different ways people can prove a run is spliced.
The interesting outcome of there being so many tiny inconsistencies in a game is that it takes a true expert of the game to effectively cheat. At which point, it gets even more sad when they do, since they clearly have the skill to actually compete.