"Yes, that is correct. They were in common use in the latter half of the twentieth century."

"And there were many such?"

"Very many."

"Had you ever problems involving presence of too many of them on trails at same time?"

"Yes. Certain times of day - when people were going to work and returning - were referred to as 'rush hour.' At such times there were often traffic jams - that is to say, so many vehicles that they got in one another's way."

"Extremely interesting. Were such creatures as whales still extant?"

"Yes."

"Interesting, too. What sort of work did you do?"

"I was involved in research on toxic agents of a chemical and bacteriological nature. Most of it was classified."

"What does that indicate?"

"Oh. It was of a secret nature, directed toward possible military application."

"Was war already in progress?"

"No. It was a matter of - preparedness. We worked with various agents that might be used, if the need ever arose."

"We think we see. Interesting times. Did you ever develop any of efficient nature?"

"Yes. A number of them."

"Then what would you do with them? It would seem hazardous to have such materials about during peace."

"Oh, samples were stored with the utmost precaution in very safe places. There were three main caches, and they were well sheltered and well guarded."

There was a pause. Then, "We find this somewhat distressing," the voice resumed.

"Do you feel they might have survived - a few, some centuries?"

"It is possible."

"Being peace loving, we are naturally concerned with items dangerous to human species-"

"You make it sound as if you are not yourself a member."

There came another high-pitched artifact. Then, "The language has changed more even than we realized. Apologies. Wrong inference taken. Our desire, to deactivate these dangerous materials. Long have we expected their existences.