Just in case opening up the leg mystifies or frightens you, here is a video to show you how it goes. It's simple and logical and works like a charm. And yes, you can use this method to open up thumbs in mittens, pockets in sweaters, etc.
by Alexandria Torres
by Kerry Timms
by PootlesPapercraft
by Reallybigmonkey1
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by vanilja
by the KBiv way