Elephant toothpaste is the foamy substance formed by rapid decomposition of hydrogen peroxide in the presence of household shampoo or dish soap. This experiment is also known as the “marshmallow experiment” due to the fluffy foam it produces! Since it’s a simple experiment with easily Elephant toothpaste is the foamy substance formed by rapid decomposition of hydrogen peroxide in the presence of household dish soap. This experiment is also known as the “marshmallow experiment” due to the fluffy foam it produces! Since it’s a simple experiment with easily obtainable ingredients, it’s a very popular class demonstration/party trick for kids. ingredients, it’s a very popular class demonstration/party trick for kids.