What does Sean say?

Overheard this morning:

Willem:  "What does the cow say?"

Sean:  "Moo!"

Willem:  "What does the pig say?"

Sean:  "Oink!"

Willem:  What does the horse say?"

Sean:  "Neigh!"

Willem:  What does the sheep say?"

Sean:  "Baa!"

Willem:  "What does Sean say?"

Sean (long pause):  "Mommy!"