"Penipeni", to be exact. That was part of the "intercourse" method of yukkuri reproduction (the other is "rub-rub", introduced during the early days of yukkuri fandom), or so the generally accepted yukkuri mythos says - a penipeni is for the "male" yukkuri, while a "mamumamu" for the "female" yukkuri (you should know how these work by now). I'm not sure about this, but I assume "intercourse" was introduced by yukkuri-Alices, who are commonly portrayed as rapists (a grotesque shadow of the complicated relationship between the real Alice & Marisa).
