Ufonaut (1865, Siberia, Russia)

While looking for a lost animal from his herd, a shepherd came across a forest glade containing a giant sphere with supports. Accompanying this sphere were a group of large, humanoid 'monsters', and his lost animal lay next to them. The cow was dead, and its stomach was slit open despite the lack of blood or gore visible on the scene. The humanoids bent over the animal, looking like they were studying it or possibly cutting something out of it, according to the witness. Later, they noticed the witness and gestured to him 'in a strange fashion', at which point he ran away from the area in fear.
Source: 'The Soviet UFO Files' by Paul Stonehill