Twasn’t blood at all. Take another look - blood coloured fruit juice, cleverly employed by Arya to fool the Waif. Acted like a mini Lady Crane suggesting the wounds reopened and voila - Waif in the dark with Arya and Needle. Job done.

The key aspect of Arya’s manoeuvre here was her feigning severe injury. The blood-red fruit juice was highlighted clearly in the sequence, for her to then use as a prop to suggest she was in worse physical shape than she actually was and unable to properly defend herself. Bolt on a little new-found acting skills…