Black bears are far from being the main threat to contestants on ALONE. In fact, the biggest threat they represent is to food storage, and since none of the players have any food in storage at this point, they don't represent much of a threat at all. Just don't do anything completely stupid and you'll be fine. Black bears tend to be shy of humans.
There are no brown bears on that island, so tapping out because of the bears is irrational - and that's what we've seen. The first guy tapped out because he was afraid. The second woman tapped out because a Mama bear's relationship with its cub reminded her of her own relationship with her deceased daughter. Bears didn't do anything to force either of them out of the game.
I have little patience for anyone who takes someone else's chance at a half million dollar prize and then quits in the first few days because of something they knew would be there when they signed up. They're both selfish pricks.
As for your question:
I don't think there's much a contestant could do to trap a bear.
First, I doubt they're allowed to. Hunting rules would come into play. (On some of the other survival shows, I've heard the contestants say that they aren't allowed to go after certain types of wildlife. Howler monkeys, which have been encountered on both SURVIVOR and NAKED & AFRAID, are REALLY annoying, what with their incessant screaming and peeing on people from above. But you can't kill 'em as much as you might want to.)
Second, one contestant on ALONE was frustrated that he couldn't find a flat enough spot to set up his camp. He hiked all over and couldn't find one. Now, if he can't find an area flat enough for that, what chance does he have of digging a pit twenty feet deep that a bear might fall into and not climb out of???
If I seriously wanted to kill a bear and only had their resources, MAYBE I could trick it into eating something I'd poisoned. Other than that, though, I think I'd just look to steer clear of the bears and hunt for easier meals. On ALONE, food is at least available. Not all of the contestants have figured out how to get it, is all.
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