The ability to find the shortest path in cases like now considered, can be useful for solving some puzzles. Here is an example of one such task.

On a tree branch a crow is sitting. At the bottom of the yard scattered grain. Crow descends from a branch, grasps the grain and sits on the fence. The question is, where should she grab the grain to the way it was the shortest.

The problem of the Raven. To find the shortest path to the fence.
This task is quite similar to the one we have just considered. It is easy therefore to give the correct answer: the crow should emulate a light beam, i.e., to fly so that the angle 1 was equal to the angle 2. We have already seen that in this case the path is the shortest.

The solution of the problem of the Raven.