The video is being made. Until it arrives, here is what it will say (120 words, about 60 seconds):

Here is the sea off the coast of California. A sea otter floats on its back, cracking open a sea urchin: a spiky ball that crawls over the sea floor and eats the tall seaweed there.

Long ago, hunters took nearly every sea otter from this coast. Then the sea urchins grew in huge numbers, and the tall seaweed disappeared. The fish that lived in it went too.

One animal was taken, and the whole shore changed. How does one change spread so far?

To find out, we will look at how to draw who eats what, and how one change reaches the other living things.

Okay, so are you ready to find out how far one change can reach?

It ends with a ready line. Then pick a reply below — any reply counts.