I don't know, gum today—when I was a kid, you could stick it behind your ear and still guarantee it'd be there nine days later. Kids of today will never know the pain of having it scraped from their hair.
Developed at Bristol University in England, the Rev7 gum is amphiphilic, which means it both repels water (hydrophobic) and dissolves in water (hydrophilic) at the same time. Sounds impossible, I know, but basically it's that hydrophobic nature which makes it chewable and consistent with other gums, but due to its hydrophilic properties, it also doesn't stick, and can be cleaned up easily.
Image Credit: Raj Deut