Do you think you're fairly observant to what's going on right next to you all the time? I would be willing to bet that you're not after watching this video.

Derren Brown sets up an experiment to see if people will notice if the stranger that just approached them is suddenly swapped out for another one. You would think it would be pretty obvious, right? Apparently that's false because very few people pick up on what's happening to them.

Watch how discrete the transition is - I mean aside from the giant poster that interrupts the conversation.

Your mind is blown now, isn't it? That's what I thought.