Trapped in a Jar

There is a study that scientists conducted which was quite interesting. What they wanted to do was put fleas into a glass jar and see what they would do. Well, of course, as soon the fleas were put it into the glass jar, they would fly away. Then what they did was put a glass lid that you could see through, on top of the jar, and they closed the jar. So, the fleas kept on trying to escape and every time they tried, they would hit the glass and they would come back down and hit the glass, and come back down, and hit the glass again.