I should note that I'm using salvaged yarn for Tom's alpaca Christmas sweater. I tried to knit him an argyle two years ago. I set it aside, picked it up again last year, and found too many moth holes to make the effort to finish it worth while. Rather than have it lie there, laughing at me, I frogged it out and returned it to the state of balls of yarn. Tiny little balls of yarn, since the moths had cut it up into little bits.

Since it's 100% animal hair, I've been using a wet splice to connect the bits. The best way I've found is to unravel four inches of each piece, overlap the unraveled bits, and let them curl up together. Once twisted, to set them as one piece of yarn, I drip a few drops of water over the whole overlapped length, twist it tightly, and roll it between my hands to get the fibers to mesh. Then I knit over the splice, being careful not to pull on it or split it in the process. Voila: invisible join.