The procedure for training rats to detect land mines was conceived of and developed by Belgian Bart Weetjens. Training starts at four weeks of age when the rats are handled to accustom them to humans and exposed to a variety of sights and sounds. They learn to associate a clicker with a food reward of banana or banana-peanut paste. They are then trained to indicate a hole which contains TNT by nosing it for five seconds. Then they learn to find the correct hole in a line of holes. Finally, the rat is trained to wear a harness and practises outdoors on a lead, finding inactive mines under soil. At the end of their training, they are tested: they must find all the mines in an area of that has been seeded with inactivated mines. It is a blind test: their handlers do not know where the mines are. If they succeed, they are certified as bomb-sniffing rats.