One of the first skills that every new knitter should learn is how to insert a lifeline into their work. Lifelines are great because if you make a mistake in your knitting you can rip everything out back to the lifeline then slip your stitches back onto your knitting needles.
Lifelines are also helpful when you are working an afterthought sock heel. Placing lifelines on either side of the waste yarn that marks the heel makes it easy to pick up the heel stitches later.
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