However, if you look at the image, your brain attempts to fuse what it hears with what it sees. The result is that 98% of adults hear the resulting fusion as 'da da'. This is called (no, seriously) The McGurk Effect. Try it yourself. If you open your eyes you will hear a different sound.
Incidentally, I don't know why, but I hear 'ga' not 'da'. I think I must be some kind of genetic anomaly.