upset

I would like to know the meaning of "upset" in the next sentence.
The tortoises, upset by the hare's manner, said, "Let's have a race and see who is faster."

A tortoise one day met a hare who made fun of her. "My, my, you move so slowly, you will never get far!"
The tortoises, upset by the hare's manner, said, "Let's have a race and see who is faster."
The hare laughed and said, "You must be joking! But all right, we'll see who reaches the other side of the hill first." Off he ran, leaving the tortoise far behind.
After a while, the hare stopped to wait for the tortoise to come long. He waited and waited till he felt sleepy. "I might as well take a nap," he thought. "Even if she catches up with me, I can easily win the race." So he lay down under a shady tree and closed his eyes.
When the tortoise passed the sleeping hare, she walked on slowly but steadily. By the time the hare woke up, the tortoise was near the finishing line. He ran as fast as he could, but he could not catch up with the tortoise.