Help with Chapter 4 frog escape example.

Frog Escape. At a local lily pond, the frogs (in Animal folder) enjoy climbing out of the water to warm up in the sun. They get a bit jumpy when a predator is sighted. In this movie, a hungry snake (Animals) wanders into the scene
The snake is off camera.
Complete the program as described.Animate the frogs jumping into the pond when the snake approaches them. Write a method that turns the snake toward a frog and slides the snake forward. Then, have the frog turn to the pond and jump in. The method should use a parameter to specify which frog is escaping.

The point of this exercise is to create some world level methods that use parameters.

What I am trying to figure out is how do I write something that lats the frigs know that the snake is within a certian distace and it time to turn and run.

Any help will be greatly appreciated.