A curious lapse in vocabulary

Stellan has started picking up language at a startling pace. There’s one word though, that to his mother’s chagrin, he hasn’t got yet.

In the car this evening he was happily chattering away to himself, mostly pointing out other cars (“Cah! Cah!”) and insisting we “Go!” every time we hit a red light. At one point he said “Daddeee!” and Emily asked him, “Can you say ‘mommy?”

“Daddee!”

“Can you say ‘mom’?”

He chuckled, which is his word for “yes.”

“Ok, say ‘mommy’.”

He thought for a moment, then let out a stream of pretty much every word he knows: “Cah! Daddee! Duckie! Doggie! Up! Dowm! Hi! Byeee! Cah cah! Go! Boo-ka! Boo-ka! Two! Five! No!”

Emily gives up.

Because I’m kind of a jerk, I said “Stellan, can you say ‘marble?’”

“Momma!”

“Can you say ‘momma’?”

“Daddeeeee!”

“Mommy?”

“Daddeeeee!”

“Mommy?”

“Daddeeeee!”

Got no explanation for that one.