Hundreds of volunteers are trying to count Bengal tigers in a mission in the swamps of India and Bangladesh.
Because the Sunderbans, where the endangered animals live, is in both countries, it was hard to tell if a tiger had already been counted.
Both countries will be working together for the first time to count the animals, which should make it the most accurate count, or census, ever.
About 600 Bengal tigers live in India, compared to 100,000 a century ago.
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