I will now tell the Panda story to illustrate the importance of the presence or the absence of the comma.
This panda walked into a tea shop and ordered a salad and ate it. Then it pulled out a pistol, shot the man at the next table dead, and walked out. Everyone rushed after it, shouting, "Stop! Stop! Why did you do that?"
"Because I'm a panda," said the panda. "That's what pandas do. If you don't believe me, look in the dictionary."
So they looked in the dictionary and sure enough they found Panda: Raccoon-like animal of Asia. Eats shoots and leaves.
(h/t to Ursula K. Le Guin - from Steering the Craft: Exercises and Discussions on Story Writing for the Lone Navigator or the Mutinous Crew)