With patience, a guitar pick and dental floss the rear case did come off.
Thank you all for your advice. In doing so, I may have damaged something:
the iPod now has a grey screen and emits 2 long beeps. Normal reset does
not help. iTunes recognizes the iPod and restored the firmware. No joy.
Still a grey screen with 2 long beeps. Google shows "2 long beeps" but
seems to be fatal.
Any opinions?
Thank you.