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When I make mine, I use curry powder rather than mustard and seasonings. Yummy! Of course, you can make it using just one egg for that quick sandwich, which is what I do. Different mustards could be interesting too - hot English, mild French or maybe a honey mustard. The important point is to plunge the boiled eggs into iced water, which stops the yolks from going green.
You can tie the knot without the ball, although it will be harder. When you jerk the rope upwards, as shown in your video, strike the rope with your index finger, about 2/3 of the way down. With practice, you will get a knot. A piece of pajama cord is an excellent rope for this method.