From blinking to your mouth becoming watery on the site of something delicious, reflexes are in every part of our daily actions. One specific kind of reflex is a conditioned reflex. This is essentially a reflex that we acquired through past experiences, for example, we as humans eat food daily and we have foods that we like and some others which we don't like as much. Whenever we see a particular food item that we previously experienced to be appetizing, the brain unconsciously works to release saliva, thus preparing the mouth for the treat!
Russian biologist Ivan Pavlov is most famous for his experiments on doggies. He states that any animal under normal circumstances wouldn't salivate but when food is presented, the doggie's mouth becomes a 'fountain'. In his experiment, he observes that when a bell is rung in front of the doggie, he/she doesn't salivate, but when a plate of yummy food is introduced in front, he does. But when after the bell is rung, if a plate of food is introduced repeatedly over time, it is encoded in the doggie's natural behavior that the sound of a ringing bell marks the arrival of food, thus salivation. After a certain period of time, he noticed that just by the sound of the bell, the doggie starts salivating, irrespective of whether food is presented or not.