During a large chunk of the book, the main character, Dana, is locked into a fridge cell and the titular egg monsters wrap all around him, supposedly to protect him from the cold. In the end, the protagonist (a 12-year-old boy) lays an egg while walking on the lawn. This means that the monsters did not really want to protect him from the cold, they wanted to rape and impregnate him.
From the same book, the fate of Doctor Gray deserves consideration. Egg monsters bury him in a sort of "egg blanket", presumably smothering him. When Dana returns to the lab, there's no trace of him. What happened is left to our imaginations. If these aliens "reward" their friends by impregnating them, what would they do to people they hate, like Gray?
The twist ending also reveals that Doctor Gray was technically justified in his actions to some extent (other than threatening Dana, of course). Gray kept Dana because he was worried that exposure to the egg monsters was hazardous, which is apparently true based on what happens to Dana at the end of the book. The egg monsters end up killing Gray for threatening Dana, proving that they can kill humans. (It is possible that the monsters only protected Dana in this situation because they knew Dana was carrying an egg.) When Gray dies, the reader may initially feel relieved for Dana, but Gray was actually holding off an alien invasion.
