"If I listen to him, we get into a lot of trouble. We play pranks and some people get angry with us. Then, we get sad because we don't want to upset anyone, the thing is we can't stop, and few people understand that." This story is a personal account of childhood hyperactivity. Told in the first person by a child, Javi, who can't concentrate or always follow rules, even if he wants to, because there's a marmoset (his hyperactivity) that always follows him and incites him to play pranks continually. A note on hyperactivity closes the book.