The thumb, that opposable digit that helps seperate (some of) us from the apes
the instrument relied upon by hitchikers around the world
It used to signal life or death for a vanquished gladiator
it allows the playing of dozens of electronic game devices
a valuable part in the pitching of a baseball
but it absolutely, positively should not be used to muffle the sound of the bolt closing on the M-1 Garand.
(trust me on this, and you may quote me as well)