question

well, in this case it's when the base of the penis swells up (kinda like dogs do) so it can not be removed from the entrance point (the anus in this case). usually happens to ensure pregnancy and can take up to 20 minutes for the "knot" to go down and be safely removed from his female :)

if the knot if forcibly removed it can also cause a tear and serious damage to the partner

thank you :)