WTF? Science or ghost? Please explain this!!!

So last night I got up around 9pm to get a glass of milk. I got the last of the gallon and we the empty jug on the counter. Next thing I know I heard what sounded like a drip. I'd the sink dripping?! I didn't turn it on. So I turned on the light, no not the sink. Wait, WTF, the lid is popping repeatedly, ON ITS OWN! You'll notice it slows down until I sit the empty jug on the dish water and float the jug, it than speeds up. I didn't mean to knock the lid off, but I couldn't get it to do it again, nor have I ever seen this happen before. The only thing that may be unique here is that the milk was raw milk... not that that should matter. If anyone can explain this please let me know.