A sport utility vehicle belonging to two intruders at Heinz Field wasn't the only conveyance to require the services of bomb-sniffing dogs yesterday morning.

About seven hours after two CMU students caused a stir at the stadium and the Joint Terrorism Task Force swooped in with four bomb dogs that alerted on the students' Lexus, another bomb dog alerted on a trailer parked Uptown at the Mellon Arena.

Was there a connection? Were terrorists targeting public facilities here? Were we all in mortal danger?

Doesn't seem like it.

The Ringling Brothers and Barnum & Bailey Circus was in town, and while Pittsburgh police were conducting a security check at the arena, a dog alerted to a particular trailer. Circus employees opened the trailer for officers and found it empty.

The employees explained that this particular trailer is the one used by none other than - The Human Cannonball.

As a Pittsburgh police report helpfully instructs, "The act uses a live cannon to fire a man through the air."

Officers from the Special Deployment Division, called to the scene, confirmed that residue from the cannon could cause the dog to alert.