Simplify the following text for a Grade 7 native English-speaking person.
Original: One of the guards , Petar Brzica , reportedly cut the throats of about 1,360 new arrivals with a butcher knife that became known as srbosjek ( `` Serb-cutter '' ) .
Simplified: One of the guards , Petar Brzica , boasted cutting the throats of about 1,360 new arrivals .