The links are viruses i think
To be honest, I'm not entirely sure if it would be considered a complete sentence or not. Technically speaking it has a subject and a verb, but I don't know if it has a complete thought. I think it should read: The clouds looked dark.
Answer:
It is a pun.
Explanation:
This is because it is a figure of speech that exploits a word's meaning in this case that the book was impossible to put down.
