A Small Misunderstanding

Yesterday as my son and I stopped at the store for a few emergency items, we saw a group of teenagers. One boy had a pretty significant case of acne. My son, who has not yet learned not to whisper -- or, better, keep quiet -- when he notices someone unusual (to him), asked me, "Why did that boy have those red bumps?" I waited until we were out of earshot, then told him that sometimes teenagers get red bumps on their faces, called --

"Called smallpox?" he asked brightly.