Word Ladder Lyric: From Open > Shut

When pies, like cases, open: that’s when birds begin to sing.
Once pies go in the oven, then those birds cannot take wing.
When pies are mere ideas, even then I pooh-pooh cakes.
Not every lad and lass can boast an Uncle Sven who bakes.
If Sven won’t don his apron, then your Sten you’ll need to arm.
No doubt you’ll need to stun Sven only – not do lethal harm.
When piemen choose to shun their duties, you’ve no option but…
to force the guy to make a pie. (With that, this case is shut.)