Use your knuckles to remember each month’s days

Count the months on your knuckles and the grooves between your knuckles. Leave out your thumb knuckle. Every month that lands on a knuckle is 31 days, every month that lands on a groove between knuckles is 30 days (or 28 for February).

Clever way to remember which months have 31 days and which have 30. Here is the one hand version: