This is one of the more unusual designs we've seen in an egg slicer. It has a scissor action. I would assume you lay the egg (or mushroom or other soft item) in the lower cup, then squeeze to bring the wire cutters down.
Made of cast aluminum, or perhaps pot metal. The only markings I've found are "Germany" on the hinge. By this, it must have been made before WWII, probably in the early 1930s. In amazing condition for the age. Looking at the photos, I should have cleaned it up a bit, but we like to mostly leave things as we found them.
Unusual kitchen item to collect, or perhaps even use.