I'm fascinated by optical illusions, but this is the first audio illusion I've heard of. The video (at 0:32) first shows the man saying "Ba Ba Ba." Then it repeats the same exact sound but shows a video of his mouth pronouncing "Fa Fa Fa." And despite knowing in advance this is going to happen, you'll hear "Fa Fa Fa" even though he's saying "Ba Ba Ba." You can't make it sound like "Ba Ba Ba" unless you close your eyes.
It's an audio queue that APPEARS to be infinitely ascending in pitch...but it's not.
Neat! According to Wikipedia, it's used as the sound of the Batpod in The Dark Knight and The Dark Knight Rises, in the music of the endless staircase in Super Mario 64, and at the end of I Am The Walrus and Echoes among others.
Also, there's a discrete version (as are some of the examples above) used throughout the Autechre song Dial.