Callback to a joke that clearly tickled Pa but was never given in full
Probably turns on references specific to the USA, where Pa lived at the time. The putative punchline is:
… you’ve got your nuts to hide
Pa – 1970s
Noel King – father of Naomi
Pull your pants up is the US equivalent of UK’s Pull your socks up (ie Get on with it).
Mr Squirrel is not a reference to Sebastian Meschenmoser’s Herr Eichhorn und der Mond (Mr Squirrel and the Moon) which wasn’t written until 2015