Erin's seizures are sometimes pattern-induced, says her mother, Theresa Leth, from the family home on Manet Avenue in Quincy.

Some patterns, such as the fabric on a couch, blacktop on the street, a window or a television screen, may induce a seizure that sometimes causes Erin to fall and her body to contort.

Boggie is one of 200 or fewer seizure-alert dogs in the United States. He is trained to keep Erin from walking too close to windows or televisions by getting between her and the items with patterns. If Erin does not see them, she may not have a seizure.

"Boggie is a good dog," says Erin's father, Phil. "He is of great importance."

And not only does Boggie sometimes prevent seizures, he can sometimes make them pass more quickly.

"Erin does not like to be licked by Boggie," says Theresa Leth. Boggie is trained to recognize the seizure and then lick Erin, which gets her thinking about something other than the attack, sometimes reducing the length and severity of the seizure.

But Boggie doesn't stop there. He can sometimes determine a few minutes in advance that a seizure is about to occur, and then warn nearby humans. Those who experience epileptic seizures often do not know they are about to occur, and many times they do not even know they have just had one.

Before Erin's seizures, Boggie sometimes will either nudge her, or walk over to family members and nudge them, thus notifying people that she is about to have an attack, says Theresa Leth.

The family members are then able to make sure Erin is safe.

"Boggie helps us in that we do not have to watch Erin as much," says Phil Leth. "Without the dog we would have to follow her from room to room."

Experts are unsure how some dogs are capable of recognizing seizures in advance, but one theory is that when people are about to have a seizure, an odor emanates from them that dogs can detect, but not humans.

By alerting their owners of an advancing seizure through nudging, licking, barking or other behavior, seizure dogs can give people with epilepsy or other brain malfunctions time to prepare themselves by making sure they are in a safe place or position.

If driving, they can pull over and continue their journey after the seizure passes; if at work they can head to a bathroom where others do not witness the attack.

It gives those with seizures a chance for a normal life, to leave home and feel safe.

"Before a seizure, some abnormal activity is going on in the brain," says Dr. Steven Schachter, a professor of neurology at Harvard Medical School and the former chair of the Epilepsy Foundation of America's professional advisory board. "It's conceivable that this may result in sweating or some kind of unusual secretion that a dog can perceive by smell."

Judi Bayly, of Amherst, N.H., another owner of a seizure-alert dog, believes that one reason the dogs act differently and notify others of an impending attack could be that they love their owners, are worried and know trouble is soon to come.

"I love my dog," said Bayly. "He has given me a bond better than that between a child or a husband."

Very few dogs that are chosen at random are capable of developing this ability, but chances are good that an agency can choose a particular dog that will eventually become a seizure-alert dog.

However they do it, Erin Leth is able to lead a much more normal life as long as Boggie is by her side.

"She's a good kid with a heart of gold," says Theresa. "She is very caring about other people."

Says Erin, "Boggie is my best friend." And by the look of Boggie resting by Erin's side, that feeling appears to be mutual.