Also known as Burning Blood.
Before a challenge either bidder may announce he is expending up to three Blood to provide Physical Traits gaining one Physical Trait for each blood Trait spent (subject to generation limit), at any time before the Test. These apply to both initial bids and to totals in the case of a draw. These Traits are active for up to five minutes after the end of the last challenge in a conflict.
This is an advanced rule from within The Challenge System.