The tusks that clashed in mighty brawls Of mastodons, are...

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