the gut hook is used to open the hide...you make a small hole then flip the knife over and put the gut hook in that hole and pull the it to slice open the hide...
never really used one or seen a use for one..
honestly, you dont really need much of a knife or anything fancy to gut a deer...
ive actually started to use a small knife...i use a Buck 311 i think...its a "trapper style" knife...2 blade folder...one with a very nice sharp point and the other with a rounded point(forget what that blade style is called)
both blades are thin...but i really like it...
most guys use WAY too much knife...big fixed blades etc...IMO they are useless and more of a hassle than they are worth for gutting a deer...
i gut my deer differently than alot of guys...i started doing alot of drives and gutting deer is burning daylight...theres only 2 of us in the crew that are "approved" (lol) to gut deer on drives because it takes everyone else too dang long...i'll have someones deer gutted before they have the tag filled out...theres no need to be a surgeon...and yes, im still clean and pretty neat about it...but theres only 3 major steps...cut the critter open...cut the windpipe...cut around the anus...everything else pulls/spills right out...a few extra cuts like the diaphram n such..but thats really about it..
a big knife just gets in the way IMO...i can work my small knife right around the anus and reach into the cavity to cut the windpipe much easier and safe with a small blade than i could a large..and its easier to make sure i dont hit guts or bladders or stomachs with the small blade...
the key is a VERY sharp knife...scaple sharp...
the other guy that guts on our drives uses a razor blade..which IMO is too much trouble because he still gotta pull a knife out to cut around the anus...he just dont like sharpening knives..but works great till that step...