You may noticed that I faltered because his dad was singing lyrics slightly different from those that I learned in school.
It is then traditional to shout "Mordida! Mordida!"... and the birthday boy takes a bite out of the cake... or if he hesitates his face would be pushed into the cake. (That is a job in which Ezra normally takes delight.) Since the cake was covered with shavings of white and dark chocolate, Alejandro's face was not covered in frosting after taking his "mordida".