The Story is from the Sutra of Parables, told by the Buddha in a sermon:
Once upon a time, there was a turtle living in a pond. Because of the very dry
weather, the pond was drying up and the turtle got out of the pond to ask for
help. He saw two ducks passing by and shouted out, "Help! Would you please
bring me to a pond full of water?"
"How can we help you out?" asked the ducks. "We are flying in
the air and you are swimming in water."
"I propose that both of you carry each ends of a piece of stick with you
by your mouths, " replied the turtle. "Then I hold on to it at the
middle with my mouth. You can then carry me to a pond full of water."
"That is a good idea," said the two ducks. "We will help you
out. But you must remember not to open your month."
So, the duck carried the turtle across the country side toward the lake. As
they passed over a village, a group of children looked at them and bursted into
laughter, "Look! What a funny sight! Two ducks carrying a stick with a
turtle holding onto it with his month!"
The turtle was angry at the remark and reply, "you guys are stupid. What
do you understand?" But, once he opened his month, he fell from sky and
crashed to death.