Look i get what your trying to do and it's smart, but i'm "trying" to get it through to you so you don't mix it up with a sensing technique or make it an invalid basis, you can say like i said that the Sealing formula is moving when the kunai is flying so you can feel it and then use the tracking technique to make sure but alone knowing that someone moved the kunai isn't valid, what if a strong wind moved it, a bird, an animal..etc, but the FTG seals are different, you missed the previous part of the video that you posted, it shows when Minato deflected the katana of the Iwa ninja and tagged the upper part of his right foot with the FTG seal, it doesn't move to Minato's will, that's simply when the seal formed on his leg after a while when Minato tagged it, it can "appear" according to his will, not "move"