This is another case of the mills putting out a piece of carpet even they didn't know how to install. The problem was solved by a frustrated installer out in California named Don Berry. He was on a job with a piece of that multi-colored shag and was, shall we say, less than pleased with the way his seams were turning out. Racking his brain to come up with a solution, he found himself looking at a discarded piece of scalloped crown molding and had an "aha! moment." His thought was that if the seam line wasn't straight, the colors would blend and everything would be hunky dory. He was right.
Using a Serpent Edge is just like using a regular straight edge, with a small difference. When following the curve of the Serpent Edge keep your wrist still, let your elbow swing in and out. This keeps your blade following close to the edge of the tool. Of course be careful not to shear the naps when you are cutting.
When you look at Photo 2 notice that one end (with the nail hole for hanging it up) starts with a convex (out) curve and the other end starts with a convex (in) curve.
If you label your Serpent Edges ends A & B, or 1 & 2, or I guess Bob & Fred if you want, it's easy to cut the edges so the curves match (Photo 3).
Of course you seal the seam as usual. As you know from past articles I am a fan of the hot glue tips for sealing edges. This was kind of fun following the curving edge, kinda like a roller coaster...hmm I think I need to get out more. (Photo 4). You will take a little more off with a Serpent Edge than a regular straight edge, about a half inch. But, the finished seam is worth it (Photo 5).
Oh yeah, I almost forgot, another benefit of the Serpent Edge: it stops seam peaking! The way the cut edge curves back and forth across the center of the tape eliminates the hinge line a straight seam gives you (Photo 6). Not something I would use on a Berber, but, I already offered you a solution for that (see FCI article on "Berber Seaming and Some Final Thoughts on Seam Peaking").