There are three turtles on their way to a spring

[Harry]

There are three turtles on their way to a spring
She is extremely thirsty. They run for a year, two years, three years and finally they arrive.
The first two turtles eagerly want to jump onto the water, but the third one realizes that they have forgotten their drinking cups.
"Oh, that doesn't matter!" says the first turtle.
"I'm so thirsty!" complains the second turtle.
"No, no," says the third turtle, "that's not possible without a drinking cup! Where are the manners! Watch out, you wait here and I'll go back and get our drinking cups!"
The others have to accept it willy-nilly, sit on a stone and wait. They wait a year, two years, three years... Then one turtle can't stand it anymore and says to the other: "Well, I don't care about anything now, I have to drink something now!"
She goes to the spring and just as she's about to take a drink, the third turtle comes out of a bush and says: "Well, if you cheat, I won't even start!"

[Zippy]

I guess I'm dense. I don't get it. haha