This was über interesting! I had to do searching to see if you could do this! (but then I remembered Animal was a module) --- so you can only do this if it's a module.

If you want to see on a class basis, you would:

```ruby
train.is_a? Vehicle
```

Another way to accomplish this is to not tie it to the Animal interface (the module), but instead take anything that behaves like you expect.

here, you are expecting that the 'animal' has an acceptable_food, and that you'll sample it.

so, you could:

```ruby
def food_for(animal)
  if animal.respond_to?(:acceptable_food) && animal.acceptable_food.respond_to(:sample)
    animal.acceptable_food.sample
  else
    []
  end
end
```