Don’t be fooled by the white-throated wood rat with its big, brown eyes, petite round ears and fluffy snout. This seemingly innocent ball of fuzz is a Southwestern menace. And it can cost you.

Then, all of a sudden, he felt as though he was looking at an optical illusion: When he viewed the squirrel one way, he saw a squirrel; when he viewed it another way, he saw a rat. “I kind of ...