Read this excerpt from A Black Hole Is NOT a Hole.

Just outside the event horizon of a black hole, light's energy keeps it zipping along, like that fish swimming along the outer edge of a whirlpool. Although the black hole's gravity changes the light's path, the light doesn't swerve into the black hole.

What does the description help readers understand?

why fish swim along the edge of a whirlpool
what happens outside an event horizon
how energy changes a light's path
where light energy comes from