Uh oh! Your stomach really hurts.You're feeling queasy.And you know what's coming next.But did you also know that these feelings are the start of a battle?A germ, probably a virus, is attacking your intestines.So your brain sends a message to your stomach to get rid of its contents.You throw up.Goblet cells launch into action, flooding your intestines with mucus.Then you have diarrhea to wash away the viruses.The experience may not be pleasant, but...