In the 1970s, David Premack wondered if a chimpanzee could be taught to ask a question. He taught Sarah 130 plastic word-tokens. She answered his questions easily. After years of work, she had never asked one of her own. Sixty years later, no signing ape has. A four-year-old human asks about 25 questions an hour. Paul Harris at Harvard counted them: kids ask their parents around 40,000 questions between ages two and five. Premack even worked out a method for teaching an ape to ask. Hide a snack the chimp expects. Wait for her to sign "where is it." He never bothered running it on Sarah. She spent her sessions answering his questions, never asking her own. A normal kid, he pointed out, asks "what that? who making noise? when Daddy come home?" on a loop. Washoe the chimpanzee, the first one taught American Sign Language, knew 250 signs. She could request food. She could sign her name. She once saw a swan and called it "water bird," a sharp invention for an animal she had no sign for. She never asked what the swan was, or where it came from, or anything else. Koko the gorilla knew about 1,000 signs. Kanzi the bonobo understands more than 3,000 spoken English words. Nim Chimpsky, Herbert Terrace's chimp at Columbia (named to mock the linguist Noam Chomsky), strung 125 signs into more than 20,000 combinations. His longest stretch was "give orange me give eat orange me eat orange give me eat orange give me you." He never asked a thing. Joseph Jordania, a researcher in Melbourne, thinks this is the line between us and them. To ask a question, you first have to know that the person across from you knows something you don't. Apes do not seem to get to that step, even after a lifetime of being talked at by humans. Human kids cross that line around their fourth birthday. Apes never do.