I'll admit that I shamelessly stole this from Reddit. However, I thought it was really cool and thought people here would be interested in a 'optical illusion' that you can't understand.
I was also hoping to get a non joke answer to my serious question: Would people who speak different languages (with possibly different base sounds) not have this problem?
Do you know of any languages offhand that don't distinguish between voiced bilabial plosives and voiceless labiodental fricatives? I sure don't.