Does anyone know what this clip is from, classic Sesame Street, Childrens late 70's?

I remember an animated short of a kid who's mom puts him to bed and
then a giant shadow appears on the walla and starts dancing around and
singing:
"Did you ever wanna be an alligator, alligator..."

I think he calls for his mom but when she turns the light on it's
gone.
I think it turns out to be the dog.

I am just writing this from memory, the last time I saw it I was
probably 9 years old.