There is a well-known chemistry demosntration refered to as Elephant Toothpaste. It has nothing to do with elephants or toothpaste; it is a safe explosion used to explain the concept of a catalyst. I did the experiment inside a pumpkin at OMSI, because that is what you do at a science museum in October.
The chemicals used for the demonstration are: concentrated hydrogen peroxide, soap, and potassium iodide. We pre-carved the pumpkins and placed the eyes and mouth pieces back into the pumpkin. Once you combine the chemicals, you have a couple seconds to put the lid on the pumpkin and hold it down. The pressure will build up rapidly and push the eyes and mouth out of the pumpkin forcefully, hurling the chunks about 6–8 feet.
I mean that is what is supposed to happen, I did not manage to place the top back on fast enough and this happened: