As a function of bloodbending, Amon can feel the councilman's hands move. The same way a particularly sensitive earthbender can interpret vibrations in the ground, so too can a powerful bloodbender sense the changes in a body, liquid life flowing though arteries, veins, capillaries. Power swelling from the mind, moving through hundreds of channels to manifest as fire, air; to twine with water and earth.
Amon knows the shape of people, and he finds them wanting. A skilled healer repairs chi flows, as many as there are in a human body; he only needs to seal one.
Noatak, with a single exception, really couldn't care less.
The shape of this one man among millions is familiar to him.
Noatak had rigged the boat just so, knowing that even their father wasn't skilled enough to rob Tarrlok of his inherent righteousness, his compassion and ingenuity-- only to bury it until it could claw its way back to the surface.
When they escaped, he'd resolved to live out the remainder of his life with his baby brother; in the split second before shrapnel tears into his back, Noatak decides that he's succeeded.
(It's all he ever wanted anyway.)