Crazy tic tac bounce!? | EVERYDAY MYSTERIES

I have a sort of physics question..... 
I try to get the last little bit of food/liquid out of any bottle/jar that I have. So... I turn the bottle/jar upside down and let the food/liquid settle. How come.... when I open the bottle/jar (It has to be plastic for this to work), the is an explosion of pressure. WHY?? It's as if somehow that excess air gets into the container, or maybe the container changes shape which cause the excess pressure? If you can figure this out... you really are a genius.