The Strangest Thing

This morning Abe called me into the kitchen to see something very strange...
He had just poured himself a bowl of cereal and after adding the milk he put the milk jug down. This is where things get weird, our milk has a snap on top not one that screws on. He had sat the lid on the top of the milk but didn't push it down shut. Suddenly it began lifting and dropping all by itself!!!
I came in and saw it for myself, it would lift up just slightly on one side and then drop back down. It lifted enough to make a small sound each time. Abe did it again another time to see if it was just a fluke and it did the same thing again. So either our milk is possesed or there is some scientific explanation for this phenomenon. If you have a snap on milk jug in your fridge right now, try it out and let me know if it happens to you to. Or if anyone knows why this happens please let me know, I am very curious.