Point taken. Although I still don't understand why having omnidirectional vision, highly proficient sensory abilities, a chameleon summon which can stay behind him while going invisible, and the ability to coat his body with Asura defence and Preta path absorption barrier wouldn't be capable of reacting and defending against the tag. He should notice the tag given it contains some chakra within it and another animal glances at him.
Because its instant. Nagato isn't as fast as instant so he gets blitzed.
There is no proof that chakra emanates from the marking. Juubito didn't notice that he was marked by Tobirama until it actually happened. Sealing formulas are written by using up chakra, but chakra doesn't stay in them.
What do you think of this scan though [You must be registered for see links]. Energy could be referring to chakra as I doubt there could be any other implications to it. It would imply there is some chakra still present within every seal.