You have three boxes filled with candies. One jar is filled with banana candies, one jar is filled with lemon candies and one jar has apple candies.. All the jars are mislabelled (i.e. all the jars have wrong labels about what kind of candies they contain).
All the candies look very similar in shape, size and color and they even smell the same. The only way to distinguish them is by tasting.
You have to eat one and only one candy to determine the correct jar labels. You can eat that one candy from any jar you want as long as you eat only one in total.