On accidentally stapled my finger, removed it as normal few days later noticed this black line. What is it?

A place for medical professionals to discuss anything wound care. Any wound care advice given here does not replace the opinion of a medical professional. If you have a significant concern please see a physician for a proper assessment.
On accidentally stapled my finger, removed it as normal, few days later noticed this black line. What is it?

/r/skin is all about the body's largest organ, protecting it, improving it, repairing it, and seeking help for it.