When did Victoria Seras figure out she can make her blood do things? I noticed she was able to do this after drinking Pip Bernadotte's freely-offered blood. when she was about to die from not wanting to drink blood. after she drinks it her left arm is replaced by a mass of chaotic black and orange shadow matter that usually manifests as a whip-like tendril. 

When in the world did she learn how to do that. I have watched it over and over again trying to figure out when she knows she is able to have that happen.
As far as I have read the manga, I think it's not a learned ability, but rather a power to show that by drinking Pip's blood, she became a full-fledged vampire, so her body started to heal and she became more powerful. Also it seems that the tendril acts on instinct rather than her direct will. Hope this helped.