Ya that's brown rice falling out. These bags were supposedly designed for sport bikes with upright facing exhausts and apparently are specially lined to be heat resistant and able to sit in front of the exhaust.

Came home from a grocery run to find that my frozen salmon fillets were fully thawed, my sweet potatoes transformed into baked potatoes, my cinnamon sticks became charcoal, and my rice bag melted 🙃

I've done groceries maybe a dozen times with these bags without issue but I guess the bag got a little too close to the exhaust. I spent all day today scraping dried molten plastic off my exhaust pipes and trying to pull rice out of my exhaust baffles (only got 2 grains out 😣).