Green’s Dictionary of Slang

to join in singing a chorus., e.g. in a public house.

1844

New Sprees of London 15: [T[he mangling is done cheap ; and whoever goes to hear a good song, may often stand a chance of getting disappointed [Ibid.] The casey that used to be the theatre, alias the mumming crib, is now the hang out of the [...] pawney belchers, or teetotallers. Here they mangle and do the chanting dodge.