The book that David throws at Jesper is a copy of the "Shadow and Bone" novel, written in Ravkan. It is owned by the original author Leigh Bardugo.
The episode title refers to a Suli saying uttered by Inej Ghafa in the Six of Crows duology. The full quote says "The heart is an arrow. It demands aim to land true."
During Inej's fight with the Inferni, Amita Suman cut her finger deeply on the woman's metal belt, and as such has a scar which she dubbed her 'Inej scar' and is actually rather proud of.