My new boss Tina sent me a bunch of optical illusions, this was the best one I hadn't seen before:
"Concentrate on the cross in the middle, after a while you will notice that this moving purple dot will turn green!
Look at the cross a bit longer and you‘ll notice that all dots except the green one will disappear."
ps - blogger image upload converts GIFs to PNGs seemingly which is why the image has been static for 24 hours
pps - if it isn't working and you've had a few drinks, try closing one eye ;-)