A squirt gun (or water pistol) is a type of toy designed to shoot water. It works on the same principle as a spray bottle. The body of the toy is essentially a container for water, and the "trigger" is attached to a pump which squirts water out of a tiny hole at the "muzzle."
In the US, for several years, import regulations and domestic laws have required squirt guns to be made of clear or tinted transparent plastic. This is to prevent them from being mistaken for actual firearms.
