Originally Posted by
jackal
It seems natural once you get to know it, but at first, keeping hold of the knife with your right hand and never setting it down actually kind of looks slightly uncouth, since it looks like you are so hungry you can't even take a break to put your utensils down. Someone who never sets his or her utensils down in the U.S. is regarded as an aggressive eater.
Maybe it's just evocative of this kind of image signifying a hungry person:

You still put the cutlery down on the edges of the plate between each mouthfull, but you pick both the knife and the fork up together for the next bite.