Snap Judgment #7: Incessant Bloodhound Gang
#435: Bloodhounds can track a man by smell for up to 100 miles
Verdict: True (more or less)
Here we are discussing smell again, but whatever. BLOODHOUNDS ARE SO COOL. Seriously. They are crazy good at sniffing things out. The specific claim "up to 100 miles" is hard to pin to the very number, but they have reportedly tracked a scent for up to 130 miles according to PBS, so Snapple probably played it somewhat conservative at 100 miles. In addition, "their extraordinary ability to discern a cold trail has sent them on fruitful missions, following tracks over 300 hours old.”
Bloodhounds have up to 230 million olfactory cells (40 times more than humans). Their sense of smell is so good and so reliable that it is admissible in court as evidence. According to that same PBS article, one famous dog, “Nick Carter” (yup, Nick Carter), led to the capture and conviction of over 600 criminals.
In order to really put them to the test, Mythbusters took a crack at trying to fool bloodhounds as shown in movies: running in random directions or zig-zags to throw off a pattern, running in a stream or other body of water to throw off the scent, and other commonly depicted techniques. Despite their best efforts, they were unsuccessful, and the ever capable Morgan tracked him with little issue. Having learned their lesson that bloodhounds are friggin' awesome at finding people, they tried again. This time, Jamie threw fish on the ground to throw off the scent and distract his pursuer. He also attempted to mask his scent with various products and suits as well as cross an even larger body of water than the first time. Once again, the able Morgan found him with little trouble.
So there you have it. Bloodhounds are coming to get you - AND THERE'S NOTHING YOU CAN DO ABOUT IT.
Cool technical piece by CIA on usefulness of scent in investigations