The Beowulf poet doesn’t describe Grendel and his mother’s appearance because it makes people imagine how the giant monster is supposed to look like. Yes, the poet should have left a brief description of their appearance. When people can imagine the monster’s looks they can make it look scary by their standards. People have different ideas of what they would find scary, and if they get a detailed description of a monster they might not find that monster’s image as scared as it could be. They can imagine if Grendel’s claws are strength and sharp like a knife or are curved and thin like a cat’s claws.