Sforno on Exodus 4:26/ספורנו על שמות ד׳:כ״ו

1וירף ממנו, he released him partially, but not totally, as until the second part of the circumcision, the פריעה, the uncovering of the corona, had been performed the ritual is considered incomplete, and not valid.

2אז אמרה חתן דמים למולות, when you were a bridegroom you said that the circumcision involves the removal of some blood during two stages of the circumcision, first the cutting off of the foreskin, then the severing of membrane over the corona.