Well quite, I mean even if the leg was entirely waterproof you'd still have to go to all the bother of taking the shoe and sock off it. Maybe the owner thought it was easier just to remove the whole leg and put a spare one on.
D0G I'd love to see what a 'desperate' prosthetic leg looks like
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Seriously though, these people should be ashamed of themselves. They evacuated a whole class of children? Couldn't one of them have just knocked on the door and called "are you alright in there?" if they thought there was something odd going on, rather than jump to the strange conclusion that it must be a paedophile?