About ten years before Elias Howe invented the modern sewing machine, Walter Hunt introduced the chain stitch machine. The needle drew thread from the top thread source down through the material and needle plate. Underneath, a finger like gadget grabbed the thread and drew it to the side. The needle went back up and down to catch the loop forming a chaining stitch. Today dogfood and feed bags commonly are made with chain stitch machines. Pull one thread and the whole seam comes out. Good for opening feed bags -- not so good for clothes.