Unsure if bug or feature but I've noticed infected respond differently to being hit at long distances with an arrow (approx 50m).

• Sometimes they show the hit animation then continue as normal.
• Sometimes they turn and run in your direction then stop along their path and begin roaming again.
• Other times they run until they get to you.

I would have thought the first instance would be intended as the infected would not have heard the direction of their attacker.