We now know that the foreskin is a normal, sensitive, functional part of the body. Many circumcised men have reported that they have been teased because they didn't have a foreskin. Just being strapped down is frightening for a baby. The often repeated statement that babies can't feel pain is not true. Babies are as sensitive to pain as anyone else.
Most babies scream frantically when their foreskins are cut off.
Some lapse into a coma. The reason some babies don't cry when they are circumcised is that they can't cry because they are in a state of shock. Most babies are circumcised without an anesthesic. Anesthetics injected into the penis don't always work. Being stuck with a needle in the penis is itself painful for a baby, just as it would be for anyone else.