Now listen to part of a lecture in a biology class.
We have a good example of this with the skunk.
As most of you know, the skunk is a furry little mammal that can be found throughout North America.
Skunks have a very distinctive marking.
Their body is mostly black, and they have a big white stripe that runs from the top of their head,
all the way down their back, and along their big, bushy tail.
So they're very easy to see
and very easy to recognize, even from a distance.
Skunks also have special glands under their tail that produce a terrible-smelling liquid.
And when skunks are approached by a predator, they lift their tail and spray the predator with this liquid.
For example, let's say a wolf is preparing to attack a skunk.
As the wolf approaches,
the skunk lifts its tail and sprays the wolf.
That's very, very unpleasant for the wolf,
because it's now covered with this repulsive, foul-smelling liquid.
The wolf doesn't want to be sprayed again, so it backs off and leaves the skunk alone.
And from then on, whenever that wolf sees a furry little black body, with a big white stripe running from its head to its tail,
it'll recall that terrible smell,
and it'll be sure to stay