The characters keep saying that Valentine's Day is not a real holiday, it was started by greeting card companies. Valentine's Day started in 496 AD when Pope Gelasius turned the Roman fertility festival of Lupercalia, celebrated on February 15th, into a Christian feast day in honor of St. Valentine and set it a day earlier, February 14th. St. Valentine was a Roman bishop who secretly married Roman soldiers, in defiance of emperor Claudius, who though married soldiers were too emotionally attached to their families. He was executed for his actions, and became a martyr and then a saint. The fact that he secretly married lovers is how the holiday became associated with love and romance.
Brennan brings a pair of Thompson sub-machine guns (Tommy guns) to a firing range for herself and Booth. While holding one of the guns and turning, Booth momentarily points the gun at Brennan, a violation of general gun safety rules. Later, Booth fires the gun without any eye or ear protection, a violation of gun range rules.