Shaking head when eating, why?

This has happened twice. My chin kept shaking/tossing his head repeatedly more than five times in a row while I syringe-fed him critical care. He only did this while swallowing the first few mouthfuls. Some time before this, he twitched a few times when eating critical care once. What could this be? Low blood sugar, calcium deficiency or overdose, seizure symptoms, or could it be related to dental problems? He LOVES critical care, and was trying to gobble it up, so could it be triggered by his excitement? Or the sudden sugar spike....

I'm so worried because the way he did those quick shakes of the head while trying to eat just looked so uncontrollable and weird. Please help if you have any idea why! Thank you.