Why is there a smiley face on the bottom of some of your cans?

The smiley face on the bottom of the can is actually a pressure relief vent to help release the pressure of the can should it become overheated. The refrigerant in the can is a high pressure gas. As with any gas it expands when heated. Therefore you should never leave or store any cans of refrigerant in your car compartment as they could overheat and rupture the can. You should always store the cans in a cool dry spot in your house.