In a Sundays-only sequence that spanned several weeks, Pogo and Albert are trying to find the Fountain of Youth. On 4/30, as they are packing for the expedition, one of Albert's gator nephews stows away inside the mandolin (where Albert has of course packed the lunch). On 5/7, having set sail in "The Fort Mudge Flyer", Pogo and Albert have a misadventure where they mistakenly think they are under attack. The mandolin is not in the boat.
Then on 5/14, the top tier of the strip contains this exchange:
POGO: If we gone find the Fountain of Youth, we'll have to explore these li'l' islands.
ALBERT: Lookie! Here's the mandolin with the lunch and my li'l' boy nephew inside.
POGO: Last week it wasn't in the boat.
ALBERT: If you ask me, this is a sloppy comic strip.....Imagine leavin' out the mandolin!
POGO: Relax, son...we din't need the mandolin last week.