A park ranger is giving some new campers a warning about bears in the area, “Brown bears are usually harmless. They avoid contact with humans. So we suggest you attach a few small bells to your backpacks. The sounds of the bells ringing will give the bears time to get out of your way. However, grizzly bears are extremely dangerous. If you see any grizzly-bear droppings leave the area immediately.”
“But how do we know if they’re grizzly bear droppings?” asks one of the campers.
“It’s easy,” replies the ranger. “They’re full of small bells.”