Why snail mail is called snail mail...

Today was mostly spent working out the kinks with my experimental setup, camera, and software. My initial results certainly show differences in snail behavior, though I don't yet know if those differences correlate with anything. Here are the cumulative tracks of 13 snails over an hour:

Numbered left to right, top to bottom.

Most of them didn't move at all. Number 12's maximum speed was 0.7 mm/s. Hence snail mail.