Although operant and classical conditioning both involve behaviors controlled by environmental stimuli, they differ in nature. In operant conditioning, stimuli present when a behavior is rewarded or punished come to control that behavior. For example, a child may learn to open a box to get the sweets inside, or learn to avoid touching a hot stove; in operant terms, the box and the stove are "discriminative stimuli". Operant behavior is said to be "voluntary". The responses are under the control of the organism and are operants. For example, the child may face a choice between opening the box and petting a puppy.