A nervous response immediately causes hyper salivation, opening of the esophageal end of the stomach, abdominal & chest muscular stress, followed with retching & forceful ejection of contents through the mouth. (dog-health-handbook.com)
But if not forceful ejection then try to hold your breast in u or c hold to make sure milk is effectively and completely fed to baby. (gomama247.com)
For example, forceful ejection is not an issue for a baby that is drinking the milk from a bottle. (exclusivepumping.com)