Mice used to sniff out drugs and bombs

The video explains how a group of eight mice work together to detect illegal substances. They operate in sensor booths with cartridges that circulate air for the mice to sniff. If no substances are detected, a green light signals the all-clear. If an odor is detected, the mice trigger an alarm. Mice can be trained to identify various substances, including drugs, pesticides, money, and explosives.

How do the mice indicate that a passenger is clear?

List some of the substances that the mice can be trained to detect.