19. There are about 80,000,000 mines (地雷) under the ground in more than 60 countries. It is difficult and dangerous to clear these mines. About 50 people including many children were killed or hurt each day. In 2003, APOPO, a Dutch research company that trains the animals, came up with the idea of using rats to search for the mines.
The animal trainers found that a kind of rats from Africa were clever and had a sharp sense of smell. The rats were about 75 cm long and weighed about 1.35 kg, light enough to run across a minefield without setting off the mines.
In January 2004, the APOPO started this project. First, the trainers let the 4-week-old baby rats get familiar with humans. A few weeks later, the rats were not afraid of people and the things around them anymore. Then they were trained to connect a click sound with food. After the rats had learned that, the trainers then taught them to tell the difference between the smell of mines and other smells. When the rats could do it, the click was sounded and they were given a bit of banana. The method was called clicker training. "The training isn't easy," said trainer Abdullah Mchomvu. "You have to be patient. Sometimes I get angry, but then again, I tell myself these are animals."
After nine months' training, the rats were taken to a minefield. They ran across the minefield, stopped, sat and searched the ground to tell the domineers (排雷员) that they smelt out a mine. Then the mine was cleared. It had taken two domineers a day to clear a 200 m2 minefield, but with the help of two rats they could finish it in two hours.
The rats and the domineers saved thousands of lives, "The rats did this job much better than we expected. So far they have helped to make almost 2,000,000 m2 of land safe. They are heroes." said Bart Weetjens, the head of the APOPO.