vigorously_

on their own

on their own is low, too. Very low." Her face grew even grimmer.
"We're lucky in at least two respects, though. First, a single Troll doesn't have much range—no more than a few hundred kilometers. They have a greater reach when several combine, but their touch gets a lot more evident when they do. And, secondly, I'm not one of the people who can tap them, so our Troll shouldn't be able to tap me, which means he can't pick me up to know I'm still alive. I just hope he can't read you, either."
"You and me both, lady," he said uneasily. "But how in hell are we supposed to know?"
"I've been thinking about that," she answered slowly. "There's a standard test, back home. I know you don't have the technology we do, but your people can do brain scans, can't they?"
"That depends on what you mean by 'brain scan,' " he said carefully.
"Damn," she muttered. "This language problem is terrible. I'm never certain I'm saying what I think I am!"
"Don't worry," he told her dryly. "We'll be in the same boat—if you'll pardon the pun—when we hit England."
"What?"
"Never mind. Just tell me what this brain scan is supposed to scan."
"Brain waves," she said. "Oh, back home it's all one procedure that also analyzes cellular structure and all the rest, but it's the brain waves that matter."
"That sounds like an EEG," he said. She raised her eyebrows. "An electroencephalogram," he explained. "It measures electrical charges in the brain."
"Good!" Her face brightened and she nodded vigorously. "There's a distinctive spike in the alpha waves for people who can't hear the Trolls—and the reverse, we