Just to let you know, this is not a S.S (Social Studies) question. But, instead of just giving the answer.. I'm going to explain. What are the five senses? Sight, Hearing, Smell, Taste, and Touch.
Now let's start with forming an answer:
As she comes close to the babies face, the baby becomes more physically and facially active. The sense that the peppermint activated was Smell. Why? When the candy got closer to the babies face, she smelt it. Because of the strong smell a peppermint has, the baby reacted.