Pop goes the weasel!
From what I could find out, ‘to pop’ was apparently slang for pawning. However there are a number of different explanations for “weasel”. One was that it stood for ‘weasel and stoat’ (Cockney rhyming slang for “coat”) and other said weasel was a corruption of ‘whistle’ and again, in Cockney rhyming slang, ‘whistle and flute’ referred to “suit”. Either way, it has something to do with a man’s jacket
There are also opinions that the word ‘weasel’ referred to a tool used by cobblers, hatters and tailors or was something like a shuttle or bobbin, which could also be pawned.
So, the song has nothing to do with weasels popping but everything to do with going down to the pub, drinking till all your money was gone, then pawning your suit or the tools you worked with to get more money so that you could drink more.
The Eagle refers to a pub in Hackney, North London, situated on the corner of City Road and Shepherdess Walk. In 1825 the old pub was rebuilt as a music hall, which Charles Dickens used to go to, then in 1901 the hall was pulled down and the present pub built.
It’s not clear who was the author of the rhyme but one name suggested is W R Mandale.