Effluxers are fork-like objects that are used to ward off Ogres.
These silver forklike gadgets are stuck into the ground in order to provide a measure of protection from the ogres. When triggered, effluxers release a cloud of scent that damages ogres' sinuses (and isn't particularly pleasant for any nearby elves).
“...this is an effluxer—also known as an ogre repeller. One of my favorite inventions you guys make, by the way.”