The answer: way more than chicken. A chicken nugget from McDonald's is comprised of less than 50% chicken, and the chicken it does use consists of pulverized chicken skin and mechanically reclaimed meat from the chicken.
McDonald's nuggets also contain dimethylpolysiloxane and tertiary butylhydroquinone (TBHQ.) Dimethylpolysiloxane is an anti-foaming agent made of silicone that typically goes into Silly Putty and cosmetics. TBHQ is a chemical preservative and one form of butane, which you may know as lighter fluid. According to 'A Consumer's Dictionary of Food Additives,' a single gram of TBHQ will cause "nausea, vomiting, ringing in the ears, delirium, a sense of suffocation, and collapse," and ingesting five grams of the stuff could kill you.
We're still more than a dozen corn-based ingredients short of a nugget's composite, but you get the idea.