Clearly just a light-hearted story of Susan and Tom having a go at singing a song. Tom isn't as good and keeps losing his place so asks Sue to help him to get back in when he does. She makes fun of him doubting his ability, at which point Sam appears and offers to fill in for Tom instead. It's likely that a double entendre might be highlighted once it’s all shoved back in place. As it were…

Atterbury, (sometimes Luffman) was a carpenter as well as musician who worked in London at the Fleet Market in Turn Again Lane. He studied music during any leisure time he had. Being rather well left off in his father’s will, he gave up his business and retired to Teddington obtaining several prizes for his glees and catches. George III even appointed him as a musician in ordinary. However it seems he wasn’t too successful as a “serious” composer and ended up having to give concerts in aid of his dwindling finances, during one of which he apparently died. 

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“As t’other day Susan and Tom trudged along, says Susan to Tom, ‘Come, let’s join in a song.’

They straight then began but Tom could not go through. ‘Put me in, Sue,’ he cried, ‘Or else it won’t do.’ 

Sue smiling replied, ‘You lubberly lout. Put you in, you soon will be out.’ Says Sam overhearing as driving his cart, ‘Since Tom can’t keep in, Sue, let me fill the part.’”

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