What's the spookiest code you've found in your codebase?

Happy Halloween!

This week we want to know about the spookiest code you’ve seen in your coding career.

What code made you say: how did this possibly work for all these years, or broke entirely when you moved a parentheses.

You don’t have to share a code snippet (although we’d love that!). We just want to hear about the code that still keeps you up at night.