The Order of the Pipistrelle was a small, secret order within the Catholic Church. As Deacon Giuseppe explained to newly-ordained Pope Benedict XVI, the Order was almost as old as the Church itself. He claimed (without irony) that members of the order had helped St. Peter carry his baggage into what became the his namesake Basilica.
The Order performed two tasks. First, it guarded Jesus Christ, who, contrary to Christian belief, had not died on the cross. Rather, in his last moments, he was transformed into a vampire. The Apostle Peter (the first Pope) and a select few who became the Order placed Jesus in a chamber deep within the bowels of the Basilica.
The Order's second task was to oversee the one last, secret ritual each newly selected pope had to endure: to be briefly fed upon by Jesus. The new Pope lost just enough blood to satisfy the vampire. In over two thousand years, only Honorius I was ever transformed into vampire, although the Order staked every pope upon his natural death from that moment forward. Another pope, John Paul I, lost too much blood to the vampire, and died only 33 days into his reign as a result.
Pipistrelle translates as Bats, an animal often connected with vampires.