Philips Avent Natural Response Teat (3M+) (Twin Pack)Key Features Anti colic valve: Keeps air away from your baby's tummy during feeding to reduce colic. Works like the breast: The teat releases milk only when the baby actively drinks, similar to breastfeeding, which might take some time for the baby to get used to. Natural Response nipple: The nipple opening only releases milk when the baby actively drinks. Right nipple flow: Customize the bottle with the perfect flow rate for your baby. No drip