A truly monstrous monster is one the reader can associate with and to some degree understand.

That does not mean their code of morality needs to be human. In fact, it can be quite inhuman and still feel justified.

A monster's attack (and/or kill) can be explained from the mindset of the monster, the victim or a third party. Sometimes, it can feel even more monstrous if the one describing it doesn't have the full picture. Say the monster is some sort of human-snatching giant. What a bystander might see is only a huge, monstrous hand reaching through the window to snatch its prey. It glimpse a vague shadow for the body, or it might not. The act of not seeing anything distinct for the monster's body could fire up the imagination, and it could end up inventing an appearance based on its own fears mixed with its observations.

Seeing such a snatching from the perspective of a bird in flight would probably not be nearly as terrifying. At least not if the author is good at describing things in the above bystander example.

Yes, the idea for the example is kinda like Roald Dahl's classic BFG. We just had to pick something.

For monsters in general, focusing on the monster's non-human traits could also personify it. 


[u][b]EDIT: Got a challenge for you people:[/b][/u]
[b]Try writing an example of either a monster attack, or a killing.[/b]
Either from the perspective of the killer/monster, the victim or a bystander.