system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does a fruit "bruise" when dropped. What actually happens that causes the change?
gpt
When the cells within the fruit are damaged, it allows oxygen in.  When oxygen gets in to the cells, it reacts with the chemicals in the fruit in that area.  The result of this reaction is a darkened color to the affected areas of the fruit.