Dried, leftover cereal such as Frosties forms a cement which can take quite some scrubbing to remove, even with detergent. Why?

The other day I was opening a letter at dusk without the room lights on.  As I pulled the seal apart, I thought I saw small flashes of bluish light at the as the strands of glue broke. Has anyone heard of energy being released in the form of light when glue bonds are broken?  Might there be some phospherent chemical in the glue which is activated when the material is stressed?