Dr. Spock is strangely silent on what to do when this becomes your parenting situation.
There was a similar incident in which Sam had a handful of popcorn kernels in his mouth, and when I tried to fish them out, he bit down on my finger -- hard. Like, bear trap hard. My wife was outside and couldn't hear me screaming for help. I tried to massage his mouth and pleaded with him to stop, but to no avail. It was very hard to remain calm and not do anything rash until he finally settled down and released me.
Now, before you run out and demand that all autistic kids be legally required to wear those Hannibal Lecter masks, let's make something clear: By far, the most frequent victim of Sam's impulsiveness is Sam himself.
So bandage up that finger quick, because he's the one who's really in danger.
Recently, Sam wandered off without me for the first time. I was in the bathroom upstairs, and when I got out, I saw him playing with his Matchbox cars, doing his normal routine. I thought nothing of it until I heard my neighbors knocking on the door. Upon answering, I learned that Sam had gone outside, jumped excitedly on a parked car, and tried to get into the neighbor's house, all in the span of the five minutes that I was on the toilet. Thankfully, my neighbors know Sam and helped lead him back into the house without incident. We've since added a top lock to the door, but Sam running off is now something we have to be constantly vigilant about.