Bull moose go through an annual cycle of growing and shedding their antlers. The antlers are used to attract females during the rut season for mating, but they undergo various stages throughout the year.
The most gruesome-looking stage is when the antlers begin to bleed as the velvet covering is shed to prepare for the rut.
The video below shows a moose, in what appears to be a European country, with bloody antlers attacking a pedestrian. Scary.