Upturning of the big toe (and sometimes fanning of the other toes) in response to stimulation of the sole of the foot. If the Babinski sign is present it can indicate damage to the corticospinal tract. The phenotype is HP_0003487 (Babinski sign). Also known as: Extensor plantar reflexes, Extensor plantar response, Extensor plantar responses, Positive Babinski sign.