He's eating foam now

We've caught Conor several times eating foam off the jog-o-line in his classroom/therapy room. So the kid doesn't eat chicken (or any other food for that matter) but he can eat foam? And gook off the walls? (Hey, it's tough to keep this place clean enough.) It would be really funny if it weren't really sad. Where does this behavior come from?

I'm reading Strange Son by Portia Iverson and she found an individual with pretty severe autism (he's non verbal, behaviors, etc.). Yet, he can communicate very well using assistive technology and is a pretty good writer. He says he can't control his behavior that well, that his body does things without his mind controlling it.
 Sounds interesting... maybe I should use that next time I get pulled over for a speeding ticket. Sorry, Officer, my mind wasn't controlling my body. Could be all the drugs I'm taking to self medicate myself?

I'm trying very hard to not let my anger at my son's condition ruin my life or my marriage, but I feel the struggle is getting away from me.