I tried feeding Goblin a nice big (but not too big) fresh-killed rat last night. He got into feeding position, but just would not strike. So I tried a smaller rat I had that was about a third smaller than rat number one. (this one was fresh killed also) and he went for it without hesitating.
The bigger rat was definately not too big for him. But maybe he saw it as too big? He just kept looking past it as if it were not there. It was not an issue of it being too cool, as it was freshly killed. So I just tossed the big rat into the freezer for my friend's boa later on.