What to expect when introducing the Philips Avent Natural Response Nipple. It is totally natural for your baby to take 2-3 tries to get milk flowing from a new bottle. Unlike traditional bottles, the Natural bottle is designed to only release milk when your baby is actively drinking, like what happens when babies breastfeed. We have 5 different nipple flow rates for the Natural bottle. When looking for the right nipple flow rate, age is a guide, but your baby’s approach to drinking and the feeding cues they will show will help determine when to move to a higher or lower nipple flow rate.