Tension neck reflex, also known as asymmetric neck tension reflex, is reflected by human infants. This reflex can prevent the newborn from tumbling from supine to prone or from prone to supine within a few weeks after birth. When the baby lies on his back, his head will turn to one side, posing as a fencer, sticking out his favorite arm and leg and bending the other arm and leg. The side he likes seems to indicate his future habit of using his hands. This reflex was first found in the 28-week-old fetus and disappeared about 3 months after birth. If it persists, it is a brain lesion.