I read somewhere that goldfish have a memory that is three seconds long. Three seconds. That's just... HEY! Who are you?
That means that, you give a goldfish a nice bowl with a castle in it and he'll be entertained forever. He's swimming along and he sees the castle. "HOLY GOLDFISH FLAKES!" he says. "Look at that! A castle!"
He goes to investigate. Then he loses interest and heads out. Three seconds later, "HOLY GOLDFISH FLAKES! Look at that! A castle!"
Eating goldfish flakes could be equally exciting. "Wow! Look! Dinner!" Three seconds later he spots another flake. "Ooh! Is it dinner time already? Lucky me!" And three seconds later, "I'm hungry! Hope the hand made goldfish flakes for dinner!"