Today I returned home to find three men standing on a neighbor's driveway. One was the owner with his small dog on a leash. It wasn't until I had parked in the garage that I saw a big snake on the driveway as well.
It turned out that the neighbor had hired two men to bring a large defanged rattlesnake with a bite guard affixed to its face to train his dog to respond. The rattlesnake's rattle was surprisingly loud, and the Doppler effect was pronounced. For the while that I watched the training, the dog initially seemed to ignore the snake intentionally, although it would stay close to the owner's legs. At some point we later heard the dog yelp with fear.
Another neighbor happened by with her dog and said she had done the same training. Her dog had yelped as well at times, but he was apparently now able to sniff rattlers and notify her.