system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do you die when you are injected with air?

When someone injects another person with a needle, and it is filled with air, why is it that someone would die from that by heart attack (or cardiac arrest?).
gpt
Air causes bubbles, which are surprisingly strong and difficult to force through tiny blood vessels.  As the vessel gets narrower, the bubble gets pinched against the sides and it forms a plug.  When the plug is in a critical place, like a heart or brain blood vessel, plugging it up can kill you.