Warwick actually did start a scab collection once, in fifth grade, inspired by a moment of vengeful hatred for his sister (he was going to put them in her soup). He waited carefully for them to fall off in the bath, then he saved them in a Russell Stover box. After a week he forgot the whole thing.
It isn’t until sixth grade that he finds the collection, and at first he doesn’t realize what they are–they’ve mostly disappeared, leaving behind little black fragments. Even these puff apart at his touch; they in turn leave behind the smell of rust.