There seems to be a little confusion when people first enter into a preserve as what to expect so I thought it would be good have a thread listing peoples experiences.
My experiences: The only way to brush a fox seems to be to drag the brush out of your inventory and "drop" it onto a fox as they stand still by the bait (if you're really lucky you may get one as they scamper by) there is no keyboard shortcut like other actions. You can't accidentally drop you brush or trade it so don't worry about that. Try not to stand to close to other glitches as the trade option will activate and fail (see above) instead of brushing. It is good to go in groups however as one bait ignited will rain down plenty of bait for all to use. Missing causes you too loose energy and holding the brush for too long will cause it to auto brush and most likely miss.