Why Humming Makes Sam Hide Crayons?

Mia draws a nice big sun.
She uses her best yellow crayon.
Sam watches Mia draw her picture.
Mia hums a small happy song.
Sam dislikes Mia’s little song now.
He hides the yellow crayon fast.
Mia wants her yellow crayon back.
She looks under the green chair.
Sam watches her search the room.
He smiles a small secret smile.