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One Chinese superstition is that evil spirits have trouble stepping over things in doorways, so to let in the humans while keeping out the demons, some doorways have something to step over. Hazardous to humans, but even worse for demons. It's a net gain if you believe in demons who can't step over things more than you believe in accessibility or criminal liability. I'm told it's important to step over the obstacle, rather than stepping on it, to demonstrate that you aren't a demon.