When swapping places with a pet, the hero's coordinates are changed
before some tests which might disallow the swap, and if the pet was
a hidden mimic or was trapped and became untame, the attempt to draw
the revised pet or former pet would actually draw the hero and have
that mistake be visible during the message about not swapping. That
last bit only occurred when the pet couldn't move diagonally (due to
being a grid bug or to being unable to squeeze through a tight space).
Also, spoteffects for arriving at a new location took place even
though the hero hadn't changed position.
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