It is possible to snare fish passively by setting up a tension mechanism (bend branch, lever/fulcrum, etc) and by using a "two-hook" or similar trigger next to the water. Instead of a snare, you would tie a fishline and hook onto the trap. The fish bites the baited hook, and with a bit of luck gets stuck on the hook. when it tries to pull away it sets of the trigger, whereupon the trnsion mechanism pulls the fish out of the water.
You have to be an expert trap-builder to get any regular success with this, as your trigger needs to be hairsharp.
It is important to practise any traps you may need to rely on, so you can carve them within the space of a few minutes and know they work well enough to kill when needed, and not just injure (which is inhumane if it can be avoided with some practise). Injured animals will raise hell, and attract other predators within the space of minutes who will surely take away your meal before you get there.
Practise the use of traps by removing the lethal part. (Make the snare-part from sewing thread, remove the weight of deadfalls and replace with up-side-down box, etc...) Only then can you learn what works and doesn't and take away the myths surrounding some skills.
Reading over the previous posts though,.. some of the traps mentioned can't really seem to be tried out to dispell the myths without actually hurting / killing the guinea pigs involved (Provided the techniques work of course)
Regards,
Anthonio Akkermans
PS. I don't think BB-fluff will work, and if it did work, it would never be enough to spread the spark in time before it burns / melts out.