30 Days Hath September...And Every Other Month

The 31 is missing from my Velcro classroom calendar. I've had it for 4 years. Every month I change this calendar and have ever since I started teaching. It was only this month of this year that the 31 has left the building. Is this a sign of the apocalypse? Or of impending doom? I guess I'd be ok with one less day in each month. It'd make the school year go by faster.

A reward is offered for its safe return.