If you have a lot of people to question about something, and they have a motivation to lie, consider this clever use of a six-sided die.
If the farmer tossed the die and got a one, they had to respond "yes" to the surveyor's question. If they got a six, they had to say "no." The rest of the time, they were asked to answer honestly. The die was hidden from the person who was conducting the survey, so they never knew what number the farmer was responding to.
Suddenly, the number of "yes" responses to the leopard question started coming up by more than just one-sixth.
I reinvented this method, except using a coin flip, during an urban economics class. We were going to actually conduct surveys in the Detroit area and thus had to learn about the problems with surveys. However my professor didn't seem very excited and pointed out some incentive shortcomings (I was too disappointed to listen too closely), and I got the impression that this is a known method with known limitations.