Stephanie Lasca, co-founder of the firm Vertical PR + Marketing, went to use the facilities at her second-floor office and noticed the water level in the toilet was high, so she took a plunger to it, said her co-worker Holly Wells.

Lasca saw a snake's head peep out from the bottom of the basin, with its tongue flickering out, Wells said. Lasca ran out and called Wells, who was a short distance away. Wells said she opened the door to the bathroom and saw the snake coiled behind the commode.

The two women taped up the door with Scotch tape and waited an hour for an animal control officer to arrive, Wells said.

"It was terrifying," she said. "We had our feet up on the desk and we didn't know what was coming next."

All the while, they could hear the snake move around the bathroom and knock over a trash can.

After an animal control officer took it to a shelter, the 1.7 metre Colombian rainbow boa bit a handler, leaving her with a slight scratch, said San Diego CountyAnimal Control Deputy Director Dan DeSousa.

The two office workers' encounter with the boa recalls urban legends of snakes in sewer systems. Wells, a vice president at her firm, said she heard from her landlord that the snake may have come from an upstairs apartment whose occupant was on vacation.

DeSousa also said his agency has learned the snake may have belonged to an apartment dweller.

"Snakes have a very low respiration rate, they can hold their breath for quite a long period of time so for a snake to come from an upstairs unit to a downstairs unit through the pipe, I think that's highly possible," he said.

But DeSousa added that he has never encountered that situation in his 25 years working in animal control.

The snake is slightly underweight and is shedding its skin, a habitual process for the reptile, he said.

DeSousa said his agency does not plan to cite the apartment dweller who apparently owns the snake, and they simply want to return the reptile.