A method of forming an opening in a nipple for a baby bottle, comprising: inserting the nipple in a holder having an opening formed therein, the nipple positioned within the opening so that an area of the nipple where the opening is to be formed is positioned in a bottom area of the opening, the holder preventing deformation of the nipple in the area where the opening if to be formed； inserting a cutting device in an interior section of the nipple； contacting and stretching an interior wall of the nipple where the opening is to be formed by the cutting device； and penetrating the interior wall of the nipple forming the opening.
