a grizzly melon
The grizzly melon is the worst thing that ever happened to your lunch. It shows up when you're not looking and eats your sandwich so fast you can't even scream.
I brought a sandwich to school and a grizzly melon ate it in front of the whole class.
My brother's grizzly melon came to life and devoured his homework.
My dog ran away because it saw a grizzly melon in the park.