system
Given the following post, respond as if you're commenting on Reddit:
human
[Fullmetal Alchemist: Brotherhood] What exactly is a 'rebound' and why is it NEVER brought up besides the second episode?
gpt
When you attempt to bypass the laws of equivalent exchange and perform alchemy beyond what you have available, a rebound occurs.  A rebound is the alchemy process balancing itself in an undirected, catastrophic way instead of careful balance deliberately performed by the alchemist. This doesn't occur often, because most alchemists we see in the series are absolute masters of the craft, and don't even attempt to exceed the natural limits of Alchemy in this way.

Technically, the prices paid for performing human alchemy are also form of rebound (since you're attempting to perform alchemy involving a human soul, and not providing *nearly* enough in exchange for that), they just aren't referred to as such during the series.  

>!Lastly, when Father dies at the end of the series, he's experiencing a rebound.