Get Out While You Can
The person who set this prank up was actually the previous owner of this house. The OP was going to redo their carpets, but after pulling it out, they came across a message written it what is supposed to look like blood. It reads, “Get out,” with a smear of “blood” running to an intake duct.
We’d be mightily creeped out if we came across this message, even though we know that blood doesn’t stay that red for that long. Don’t ask how we know; we just do. You can also put a skeleton in the crawlspace to trick the next person to go down there. A fake skeleton!