Many species of gulls feed their chicks by regurgitating food. When parents return from foraging, the gull chicks peck at a red spot on the parent's bill, which causes the parents to open the bill and regurgitate their food. Chicks will peck at a red dot painted on any long, slender object. For the chicks, pecking is a ________ and the red dot is a __________. For the adult gulls, the chicks pecking at their bills is a _______ and regurgitating food is a ________.