Cable without a needle?

Has anyone knit the Blue Sky Alpacas Sweater Socks pattern? There is one line that has me confused. The Half Cable Pattern states:
"*P1, k3, p1, k into back of 2nd st, k first st, sl both sts off needle, k1; rep from * around".

Where is the 2nd st? And how do I knit into it?

Thanks for any help!!

The second stitch is the one that’s second from the tip of the left needle. You knit into it as normal, but you can’t slide it off just yet. After you pull the yarn through that stitch, knit into the first stitch as normal and slide them off. You’re just knitting them out of order. It works fine. Try it.

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