Pattern abbreviation: sl
Many tatting patterns require two shuttles because they require that you make rings facing the same direction as the chains face. Personally, I like to avoid using two shuttles if I can because they have a tendency to get tangled together. Besides, I'm lazy and I'll do what I can to avoid winding a shuttle.
For many of these patterns, it's possible to eliminate using the second shuttle when you use the shoelace trick. This trick effectively swaps the shuttle and working threads, so instead of picking up the second shuttle, you simply "move" the shuttle thread to face the correct direction.
Here's how to do the shoelace trick.
Cross the shuttle thread over top of the working thread. Pass the shuttle behind the working thread and through the loop you created when you crossed the threads. Pull snugly against your tatting.
This is called the shoelace trick because it's the first step you use when tying your shoes.
Simple, but very, very handy. I find I use this more and more all the time.