Dog on a Broomstick

The countdown has started for the Grand Spell Contest and the Witch's cat has run off to be a cat-food tester! Then the Dog appears on her doorstep. He can't scratch, but he can dig big holes. He can't hiss and spit, but he can growl, dribble and cover everthing in muddy pawprints. Will the Witch let the Dog help her at the Grand Spell Contest? And, most importantaly, can they both fit on her brooomstick?