Darren is trying to get his young son to eat his peas. at first, darren praises him whenever he moves his fork near the peas; after the child does this reliably, darren praises him only if he actually puts a pea on his fork; then darren's praise is only given when the child puts a pea on his fork and moves the fork toward his mouth. darren carries on this way until the child eats his peas. darren is using to get his son to eat his peas.