system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do many spray cans get cold when you shake them?

I always thought exciting a gas warms it up.
gpt
Think of it like this - it takes heat to evaporate water, right? So you have to *put energy into the system* to turn a liquid into a gas. The gas is higher energy, which has to come from somewhere. 

This is true for any evaporation, not just water. Any time a liquid changes into a gas, it will take energy out of that system (phase changes from liquid to gas require energy). When the liquid in the can changes into a gas, it pulls energy in the form of heat out of the system, and the temperature drops.