Yahtzee Croshaw, the guy who makes Zero Punctuation videos, wrote a book where jam, like toast jam, gains sentience and takes over the world. It's somewhere similar to what you described.
I enjoyed [Ben "Yahtzee" Croshaw's book Jam](www.amazon.com/dp/1595829571/). It's about a apocalypse of killer strawberry jam that covers Australia.
If it's scary Jello you're looking for, have I got the book for you!
Someone hasn't read Yahtzee's new book.