A threat you can't prove exists, unsure it even exists, or know it doesn't exist but still use it anyhow.
If you disobey me and go out in the woods at night the Chupacabra will get you and eat you. (Chupacabra is the Blind Threat)
If you don't do what Zeus commands he'll hit you with a lightning bolt and send you to Hades! (Hades and Zeus hitting you with a lightning bolt are both Blind Threats)