What reflex is characterized by the toes fanning out when the sole of the foot is stroked?

The correct choice is representative of the Babinski reflex, which is an important neurological test that demonstrates an infant's developmental stage and neurological integrity.

When the sole of the foot is stroked, the Babinski reflex causes the big toe to lift upward and the other toes to fan out. This response is indicative of normal neurological functioning in infants up to about two years of age, where the presence of this reflex is expected. In adults, a positive Babinski reflex can suggest damage to the corticospinal tract, leading to wider implications for brain and nerve health.

In contrast, the Moro reflex is a startle reflex seen in infants, which involves throwing out the arms, then retracting them and crying. The rooting reflex is a response in newborns to turn toward the stimulus on their cheek, aiding in breastfeeding. The grasp reflex involves an infant's tendency to close their fingers around an object placed in their palm. Each of these reflexes is characteristic of different aspects of infant development and neurological function, but they do not involve the fanning out of the toes when the sole is stroked. Therefore, the Babinski reflex is correctly identified as the reflex associated with the toes fanning out.