According to Billy, the ability to spit is not innate. Well, on command. Or no...
Actually, let me correct that. He's been able to spit food and water for, oh, about a year now- probably longer. If you count dribbling peas down his chin, then definitely longer. Like, today, when he was purposefully spitting water on Grandma to be silly. I don't think Grandma thought it was all that silly, Billy.
Well, we're learning to brush teeth. I'm not. I know how to brush my teeth. But he's learning. It involves his toothbrush, a stolen toothbrush of mine (lucky I have another one, and yes, it's clean) and a lot of trial and error. The brushing is more like sucking water out of the brush and asking for more water. Then I attack him with a brush while he squirms and then relents, because we're going no where until he molars are at least glanced by a brush. He's got the whole sticking the brush under the running water part down. Now he's working on spitting.
This morning he leaned his head over the sink when I did. Then he made a spitting noise. But... no spit. Just the noise. Hmm. I guess spitting is a work in progress.