Light Jigging - setup the Jig

What's the deal with that absurd looking bottom hook?  I'm familiar with the top eye "assist hook" I think they call it, but that bottom one doesn't look like it adds much to the game.  Unless it is a spring-type-deal somehow that collapses when a fish bites it?  I think the top eye hook design was to keep from hooking the hard bottom.  I've used them and they work quite well.