Sucking reflex

Babies are born with many reflexes to help them survive. The sucking reflex is accompanied by the rooting reflex. Typically, when you touch the infant’s right cheek, it turns towards the right to locate the nipple, and start feeding. The suck reflex is initiated when something presses on the roof of the mouth (hard palate). Some babies seem to suck ‘on anything’, have a very sensitive suck reflex and mothers think they are still hungry. Babies also use sucking to help relieve discomfort (or pain). There is a lot of research about the use of sucking to relieve pain for infants when painful medical procedures are undertaken in a medical setting.

Suck is a noun; sucking is a verb.