Sentence:  The boy turns into a dog and bow-wows—a cock, he flaps his wings and crows—a cow, he fetches a long drawn moo—a horse broke loose, he <WSD>curvets</WSD>, prances and kicks fearfully among his nursery blocks—a big bull, he waxes dangerous as he bellows and paws the carpet—a locomotive, he blows his steam whistle and dashes round the nursery with puffs and yells spasmodic, or taming down, sticks a feather in his cap and struts a soldier. 
Meaning of the word marked with <WSD> tags:  "Of a horse or, by extension, another animal: to leap about, to frolic.