7-Eleven is celebrating its 85th anniversary on Wednesday with its annual Slurpee giveaway. While supplies last, and at participating stores, customers can stop in to claim their free 7.11 ounce frozen drink.

According to the Mayo Clinic, one theory about brain freeze, or ice-cream headaches, is that "cold food or drink may temporarily alter blood flow in your brain, causing a brief headache. Some researchers suspect that the pain is referred from your mouth to your head via the trigeminal nerve, which delivers sensory information from the face and mouth to the brain."