From Quirky Mind Stuff, by Richard Wiseman (via Matthew Cobb), we have a bunch of illusions, most of them amazing.
There are two that you can try yourself, but you’ll need a friend. I tried them, and they both work for me, but for the “tightening thread” phenomenon, be sure that your fingers are relaxed and you’re not trying to keep them apart. The “numb finger” trick also worked for me, but didn’t for two of my co-workers.
Anyway, have a look, and report what you see for the final illusion.