Mason is the surname of a Muggle family. In 1992, the Masons visited the Dursleys because Mr Mason had to talk drill business with Vernon Dursley. While the Masons were talking to Vernon, Dudley, and Petunia Dursley, Dobby levitated the cake, which was made by Petunia, and dropped it on Mrs Mason's head. Harry Potter pretended to do this because the Masons were Muggles and did not know of the existence of magic.