Notice this young man taking his pulse. Especially at his age, this action ought to raise all sorts of red flags. What does he know that you don’t? Is he worried that he no longer has a pulse? Is he expecting that pulse to stop?
I would give him the benefit of the doubt, of course. First ask him why he is taking his pulse. Watch his response time as he answers. Watch his expression. Does his explanation make sense? If he seems confused, your next project will be to carefully lock him into your shed or cellar for a few days. Don’t let him get his teeth near you.
Many films and books deal with the problem of the zombie, but few have properly attacked the problem of the protozombie. You obviously can’t shoot this young man in the head. Maybe he really is suffering from wrist pain, helped by pressure and medical marijuana. At the same time, leaving him to wander away at this point may endanger you and your entire family.
By sequestering this possible protozombie, you can protect your loved ones from harm. If the boy in the shed becomes more lucid, rather than less lucid, over the next few days, you should be able to release him. I’d give him a good math test first, just to make sure the cognitive processes were really working.
P.S. That hole in door for inserting rats and turkey heads? Until our pulse-taker has actually gone over, I’d save the rats for later. Bratwurst and carrots and other long, round foods are the better choice to start. (A small practical note: while the absence of carrot consumption cannot be construed as proof of anything, I’d observe that eating large quantities of things like celery and carrots over the first day or two would probably be enough to convince me to unbolt the door. Zombies do not eat carrots.)