One day, a bull wandered into the forest. Drawn in by its luscious greenery, it ate until it was full as can be, to the point where the bull struggled to walk without great effort.
In the forest also was an old, hungry lion. He wasn't as fast or as agile as he once was and so the forest animals were almost impossible to catch. On spotting the sluggish bull, the lion couldn't believe his luck. He stalked the bull until he was sure he was in easy reach then he attacked and killed the bull before devouring the animal in its entirety.
Feeling now sluggish himself, the lion decided to walk back home for a nap. On his way, he spotted some forest animals and let out a massive roar. Some hunters who were close by were alerted to the lion's presence. They immediately tracked the lion down and killed him.
The moral of the story? When you're full of bull, it's best to keep your mouth shut.