Flushed Out
A 'Web of Fear' tip of the hat to the Yeti's roars - flushing, run backwards.
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"We know the Yeti are around here somewhere, but no one's been able to find them," the Corporal Lethbridge-Stewart said, clearly frustrated. "We've checked the Underground thoroughly in both directions. They've disappeared!"
"Nonsense," the Doctor said. "Yeti can't just disappear… good heavens, what's that noise?"
"Oh, some malfunction with the water-closets. They've been flushing endlessly all afternoon."
"Flushing?" The Doctor's eyebrows quirked.
The Corporal rolled his eyes. "The loos, Doctor. Now, about those Yeti… wait, where are you going?" The strange little man was pelting for the water-closets, waving his arms.
"Cordon off the loos! I know where they are!"