system
Given the following post, respond as if you're commenting on Reddit:
human
How do we know if sound cames from behind or from front?

We have two ears, so sound going from left or right is slightly delayed in one ear. I believe this is how we can recognize if sound comes from right or left side. But how can one say if sound comes from front or behind?
gpt
The ear is shaped in a very funny, but very specific way.  The shape of the ear makes sound very slightly different, depending on front or back, or even above and below (specifically not left and right, funny enough, but that's why 2 ears are nice).  The way you tell is more trained than an actual knowledge.  The sounds you hear from behind are always very slightly muffled, but your brain recognizes them as sounds it's heard before and makes them sound normal, but "from behind".  This also helps explain why sounds you don't normally hear can be hard to pinpoint the location of.  Your brain's spacial mapping plays a big role in how you hear sounds.