Terry said again, groping in his mind, "They act like fish in a closing
net. I've seen something like this once, when a purse-seine was hauled.
Those fish were frantic because they couldn't get away. Just like
these."
"Why can't they get away?" asked Davis grimly. "We haven't seen anything
holding them."
"But we heard something," pointed out Deirdre. "The hum. That may be
what closes them in."