Holly Bug is a Medical Alert chihuahua in Georgia. Since 2006 she has been warning her diabetic owner, Caroline Everitt, when she seriously must take a blood clucose reading or risk going into a coma.
At three pounds eleven ounces, Holly Bug is believed to be, as of 2009, the smallest service dog of all time. She was not originally trained for this purpose, but after the fourth time she saved her owner's life, it was clear Holly Bug had a natural ability. So she underwent training to be increasingly reliable at her task.
See More Holly Bug Pictures at Caroline's photostream