The CBSA uses passive detector dogs, unlike some other law enforcement agencies, which use active dogs. When a passive dog detects a scent that it has been trained to recognize, it sits beside the source of the smell. While active dogs, which bark, scratch, dig or bite at the source of the scent, were used initially by the CBSA, passive dogs allow the officer to circulate among passengers more peacefully, and are considered by the Agency to be more effective in the course of their work. The Passive Dog training was implemented in 1993, and is now the Agency's preference.