The dart gun is a toy of Calvin's that shoots out suction-cup darts. He owns two which he gave one to Hobbes so they can play "War and not Peace" or cowboys. Calvin once tried to shoot a horsefly that was on his mother's head. He also tried to shoot his mother in a Tracer Bullet story arc where his mother accused him of breaking a lamp. He imagined the gun to be a .45 automatic and said that it was "a friend very close to my heart, just a little down and left to be precise." and "an eloquent speaker."
He also once interrupted a get-together between his mother and her friends by shooting at the guests with the gun. Also, he once shot his dad, thinking that he was a Monster. Also, in a Spaceman Spiff strip, Calvin shot both his parents (and some of their friends, who they had over), imagining that they were caterpiller-like aliens.