I'll give a bit of background so this doesn't sound completely inappropriate. It's not uncommon for male infants to get an erection while breast-feeding. I am curious whether this happens with bottle-fed infants, because I'm curious whether it's a physical thing (the act of feeding) or a hormonal thing (something in the breast milk). This came about while I was considering that fathers don't get the hormonal changes that mothers get with pregnancy/labour/breastfeeding that helps bond them to their children, and I wonder if the reverse (the child's bond with a parent) is transferable to whoever feeds them or if there's something particular about the bond with the mother.
For parents with sons that have been bottle-fed, or anyone who might happen to know, if you don't mind answering what's probably a bit of an awkward question, did they ever have this reaction while bottle-feeding?