Some right-wing Jewish groups practice metzitzah b’peh (MBP), the oral sucking of the blood from the baby’s penis, by the mouth of the ritual circumcisor.
The problem with the practice is that, if the circumcisor has herpes, it can be transmitted to the baby. Babies infected this way can — and have — suffered brain damage and death.
Regulating the practice is difficult because of the secretive and insular nature of the groups that practice it. But De Blasio has decided against even trying, allegedly because of the political support he has received from the groups that practice MBP.
As for kissing the rabbi’s hand, that’s not a figure of speech, De Blasio really did it.
NB: Most other circumcisions are perfectly sanitary and pose no risk.