Sentence:  The Renault burst effortlessly through what turned out to be an anorexic privet, and immediately encountered something more substantial in the form of an astonished and transfixed Cheviot. McGregor heard a <WSD>gassy</WSD> – groan half-baa and half-burp – as the sheep was bounced into the air, the Renault bludgeoning onwards beneath. 
Meaning of the word marked with <WSD> tags:  Of a person: tending to burp; burpy.