Giant skin coloured finger that you put in your real thumb. Specially good for comedy acts or magic for kids.

A hilarious idea: Set up a mousetrap inside a change bag, a long hat or even on the magic table, then when everybody hears a big noise, as if something got suddenly trapped, you pull out your hand with the giant thumb caught in the mousetrap.  Sudden gag, visual and effective. Another original idea is to put on your thumb a red D-light, and then getting it into the giant finger. When the D-light is turned on and off several times, the effect will appear as if the thumb is beating of pain.