Healthy adults will drool when they eat plums. Plum is a very sour fruit, which makes people drool. This kind of reflex activity is innate and can be learned without learning, so it belongs to unconditional reflex.
Look at plum, say plum, there will be saliva secretion. On the basis of knowing the taste of plums, he saw that plums, through the participation of cerebral cortex, formed a conditioned reflex of drooling.