A student inquired: "Why did Tolkien dislike cats?"

The truth is, during WWI, Tolkien was assailed in his trench by a trained mutant cat. These were experimentally set loose on the English trenches by an evil German scientist, Friedbert Haarball von Katzenstreu. Only after a titanic battle Tolkien managed to defeat the vile cat.

The event left Tolkien somewhat traumatized. This is why he disliked cats ever after, and made an evil cat - Tevildo - an enemy in his early stories.