Knotting?

https://www.urbandictionary.com/define.php?term=knotting
There u go

Uiii ok thanks~

More specifically, it's the base of the penis that swells. That's why you don't pull dogs who are mating apart, it will injury the female.

I forgot this: Because no matter how much you try, the penis can only be released by the male dog, when it unswells.

Lastly, it's a way/technique to ensure that the female gets pregnant, because she cannot move until the male is done. So, the male is in complete control.

So, the seme knotted the uke purposely to try to impregnate the uke. Because when knotted the uke cannot stop the mating process, it has to be the seme. So, it's the opposite of using a condom. You use a condom as a extra precaution to not get pregnant and you knot as an extra precaution to get pregnant.