once in a blue moon

Tonight is the first of two full moons this month; the second falls on New Years eve.

This is called a blue moom and it won't happen again for another 18 years (hence the term "once in a blue moon").
This should make for an interesting December.

Have fun, stay safe, and watch out for werewolves.

Especially if they look like Taylor Lautner.

...

In which case you should also (probably) keep your eye out for cougars.

Daaaaiiiimmmmm!