A guy's going on a hiking vacation through the mountains out west. Before setting off into the boonies, he stops into a small general store to get some supplies.

After picking out the rest of his provisions, he asks the old store owner, "Say mister, I'm going hiking up in the mountains, and I was wondering; do you have any bears around here?"
"Yup," replies the owner.
"What kind?" asks the hiker.
"Well, we got black bears and we got grizzlies," he replies.
"I see," says the hiker. "Do you have any of those bear bells?"
"What do you mean?" asks the store owner.
"You know," replies the hiker, "those little tinkle-bells that people wear in bear country to warn the bears that they are coming, so they don't surprise the bears and get attacked."
"Oh yeah," replies the owner. "They're over there," he says, pointing to a shelf on the other side of the store.

The hiker selects a couple of the bells and and takes them to the counter to pay for them.
"Tell me something, mister," the hiker inquires, "how can you tell when you're in bear territory, anyway?"
"By the scat," the old fellow replies, ringing up the hiker's purchases.
"Well, um, how can I tell if it's grizzly territory or black bear territory?" the hiker asks.
"By the scat," the store owner replies.
"Well, what's the difference?" asks the hiker. "I mean, what's different between grizzly scat and black bear scat?"
"The stuff that's in it," replies the store owner.
Getting a little frustrated, the hiker asks, "OK, so what's in grizzly bear scat that isn't in black bear scat?" he asks, an impatient tone in his voice.

"Bear bells," replies the old man as he hands the hiker his purchases.