What is a good, funny trick to play on my brain?

Go outside on a sunny day. Stare straight off into space and keep on staring for like 2 whole minutes and just focus on one thing, don't move your eyes anywhere. You'll notice your vision will kinda start to change. Or just go to your local park, go on a swing and put your head all the way back and keep on looking at the sky while your on the swing, your brain will get kinda dizzy.