The patrol is in charge of security aboard boats in the Washington State Ferries system, because they and their docks are considered part of the state highway system.

As a result, the patrol uses specially trained dogs to routinely sniff for explosives in the vehicles waiting to board.

The system normally works well. But there was an incident at the Mukilteo ferry dock north of Seattle last month in which one of the bomb-sniffing dogs lunged at and bit a dog in a waiting car.

That has led the patrol to issue a warning: Don't interfere with working law-enforcement canines.

The incident in Mukilteo was the only one in which a K-9 dog has gone after someone's family pet, patrol Sgt. Monica Hunter told the Seattle Post-Intelligencer. But there have been other times when the dogs started to lunge after pets and handlers had to yank back on their dogs' leashes, she said.

The dogs' presence is part of the stepped-up security around ferries after the 9-11 terrorist attacks, and they and their handlers are doing serious business, so don't be surprised if they look grim, Hunter said.

"The handlers aren't out there socializing, and these are working dogs. They're looking for bombs or firearms or fireworks," she told the P-I.

As for the dogs, she said, "This is not Fluffy."

Here are the steps the patrol suggests for people traveling with dogs:

• Keep car windows rolled up and doors closed while the K-9 dogs do their work. They can smell through the metal doors.

• Do not pet, approach, feed or in any way engage the K-9 dogs.

• Keep your pets on leashes.

• Don't allow your pets to interact with the K-9 dogs.

• Understand that handlers might yank on the chain or might appear to be rough with the K-9 dogs. But this is part of the dogs' training, and the handlers often give the dogs positive feedback.

• Arrive early for your ferry trip.

• Obey the slow speed limits in the terminals' holding lanes.