So, I went out to check on my rabbits, and I found one of my nine-week-olds lying dead on the floor of the cage. More alarmingly, I found that its mouth was full of what looked like tiny off-white grains of rice. It hadn't had access to any food that looks like that. I feed my rabbits a mix of oats, wheat, and barley; they also have access to greens most days. Does anyone have any idea what the grainy stuff might be? Or the cause of death?