Can't figure out how "Coldblood" works

[Bisonfan95]

All its upgrades depend on you unlocking the first one (snowflake image). According to perk descriptions Coldblood "stacks" do you lose the stack after 10 seconds? Does the stack stays until you use it? WHERE DO YOU SEE WHERE IT IS STACKING IN THE HUD? I just see a symbol of arrows next to my health with a timer (I guess the coldblood duration) but no stacking

 

[AdamTaylor]

It lasts for 10 seconds. There should be an icon in the top left to show you that it's still active.
It can be confusing as it looks the same as icons for quickhack cooldowns. The UI is not great.

Basically you have it for a few seconds after a kill, and can get more stacks if you keep killing.