On the first day, God created the dog and said, "Sit all day by the door of your house and bark at anyone who comes in or walks by. For this, I will give you a life span of 20 years."
The dog said, "That's a long time to be barking. How about only 10 years and I'll give you back the other 10?" So God agreed.
On the second day, God created the monkey and said, "Entertain people, do tricks, and make them laugh. For this, I'll give you a 20-year life span." The monkey said, "Monkey tricks for 20 years? That's a pretty long time to perform. How about I give you back 10 like the dog did?" And God agreed.