system
Given the following post, respond as if you're commenting on Reddit:
human
[28 Weeks Later] How does an infected person tell someone is non-infected when they're over 100 yards away and sprinting?

They don't attack their own, so how do they know who to chase and who to ignore when everyone is running around?
gpt
Multiple senses, most likely.  Probably mostly smell, like a shark with blood in the water.  But the non-infected also behave differently, move differently.  

Once they detect some deviation from what they instinctively know is infected patterns, they go after it.