reflex

The plantar reflex is a reflex elicited when the sole of the foot is stimulated with a blunt instrument.

(source: en.wikipedia.org)

Babinski reflex is one of the reflexes that occurs in infants. Reflexes are responses that occur when the body receives a certain stimulus.

The Babinski reflex occurs after the sole of the foot has been firmly stroked. The big toe then moves upward or toward the top surface of the foot. The other toes fan out.

(source: nlm.nih.gov/medlineplus)