It would not be plausible for Homer, who has lived his whole life in Springfield, to have not noticed the three giant mountains that were pointed out to him before.
Grampa's dentures fit the bite mark on the frozen old mountain climber, implying that Grampa is the one that tried to eat him, not the other way around. But this climb would have happened in Grampa's youth, he would have had his regular teeth back then. So why do the dentures fit the bite mark?