The tusks that clashed in mighty brawlsOf mastodons, are...

The tusks that clashed in mighty brawlsOf mastodons, are billiard balls.The sword of Charlemagne the JustIs ferric oxide, known as rust.The grizzly bear, whose potent hugWas feared by all, is now a rug.Great Caesar's bust is on the shelf,And I don't feel so well myself.