The McGurk Effect

[bitwh0re]

The video is a person saying "GaGa", but the soundtrack is of someone saying "BaBa". Your brain is fooled into hearing "DaDa".

http://www.media.uio.no/personer/arntm/McGurk_english.html

And, "Ohhhh BABA-san!"

http://www.youtube.com/watch?v=eD4x_6HBi7E&NR=1