A few weeks back, you might have seen a video floating around of what appeared to be Viner Kevin Parry playing catch with his own reflection. It's hard to look away from, but it's obviously impossible. That led commenters to speculate on how the trick was done.
Theories were split: was it two people and no mirror, or one guy with a mirror and some VFX skills? YouTube debunker CaptainDisillusion thinks its the latter, and demonstrates exactly how to do it.
The trick relies mostly on physics. The ball is thrown so that it hits the mirror at the apex of its bounce and returns to the starting position in an identical arc. After getting one take with the camera pointed down, the throw was repeated with the camera pointed towards his reflection. Both takes were then combined, and the "duplicate" balls were painted out to complete the illusion. Captain Disillusion even recreates the trick to prove his theory (or to be an imperious jerk, you decide).
Off to the next thing we can ruin.