The Only Use of

grotesque
in
Lord of the Flies

Then they inched the grotesque dead thing up the rock and toppled it over on top.
p. 39.6

grotesque = ugly

Definitions:

(1) (grotesque)
distorted and unnatural in shape or size -- especially in a disturbing way

or:

ugly, gross, or very wrong
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More rarely, grotesque can refer to a style of art or instances of it that combines or distorts in a fanciful way natural forms into something that is often ugly or disturbing. Grotesque can also be used specifically to reference a gargoyle-like sculpture without a waterspout.