On the mating process of leeches.
In the case of Hirudo Verbana, mating takes place in the water. Each of the pair will grab onto the other, usually with one leech initiating by giving the other leech "Love Bites", with each leech lining up facing the other and "hugging"
These love bites may look like an attack at first, but the initiating leech will suction it's anterior sucker somewhere along the middle of the other leech, not causing any visible penetrative wound. This allows the leeches to properly line up and press together their sexual organs despite being underwater.
Notably, a leech that doesn't want to mate will reject another leech by dodging attempts to suction on, or weaving in complicated ways to keep their sexual organs from lining up properly until they can eventually escape.
That is to say, my tank is currently full of leech spooge