The left panel shows an old ship with missing pieces and says “...it asks the question: if you replace every part of a ship one by one until none of the original parts remain…”. The right panels shows a new but ever-so-slightly different ship and says, “...will it be the same ship? And if not at what point does it become another ship?”

The classic “Ship of Theseus'' thought experiment.  For hundreds of years, the people of Athens would take the ship of Theseus (the founder of Athens) out for a voyage on the anniversary of its founding.  Given the amount of maintenance it would take to keep an old wooden ship seaworthy, after many years, none of the original parts of the ship would remain.  Is it still accurate to call it the Ship of Theseus at that point? Image credit: Pastillustrator