system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What would happen if two people moving faster than the speed of sound tried to have a conversation. Flash/Quicksilver for example.
gpt
If Flash and Quicksilver  were running next to each other, and Flash said something, the sound would never reach Quicksilver's  ears.

If Flash was in front, Quicksilver could hear him, but Flash couldn't hear what was said back.

If Flash stopped while in front, he could hear what Quicksilver was saying, but it would be time reversed.