Everywhere rats go they leave a steady stream of urine, feces and gland grease. Within their urine and feces and gland grease are strong pheromone scents which helps them retrace their steps and attract other rats. Pheromones and steroids, such as male testosterone or female progesterone and estradiol let other rats know that there is another rat around, so it’s not that dangerous and maybe they will get lucky. Tracking odour trails is a crucial behaviour for rats and all rodents often leading to food, mates or away from danger. When rats find a odour trail they use active sampling, to sense the environment. They track odour trails accurately with near-optimal sampling – within 1 cm, and they use a multi-layered strategy.
http://gogreenpestcontrol.ca/rats-the-secret-sensory-world/
gogreenpestcontrol.ca insectandrodentexterminators.com Delta Ladner Tsawwassen B.C., Randy Bilesky BsF CPA RPF
https://www.linkedin.com/pulse/rats-secret-sensory-world-randy-bilesky/?published=t