The whole "only a dog can appreciate it" line of thought took on a new dimension for me last winter. I put a set of those deer whistles on the bumper of my car. I heard nothing, but I never had a deer jump out in front of me. They worked pretty well, or so I thought.

Several times I looked in the rear view mirror to see pretty impressive herds of deer chasing me. Upon an inspection, I determined I had installed the whistles on the car backwards. I guess that gives credence to their capability.