If your dog howls at the moon, and the moon turns blood red...
...your dog might be evil
If your dog often comes home with the blood of martyrs dripping from its teeth...
...your dog might be evil.
If your dog's eyes burn black and red like the fires of hell...
...your dog might be evil.
If Robert Johnson writes songs about your dog "being on his trail"...
...your dog might be evil.
If your dog not only sheds, but the hair turns into worms and snakes that spit venom...
..your dog might be evil.
If your dog not only barks all night, but shouts eldritch spells, and harrowing blasphemies...
...your dog might be evil.