system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do Tetanus shots hurt so much more than other shots?

I don’t think it’s just me but when I was a kid I felt like Tetanus shots were always the worst ones. They’d hurt more the day of and for a few days after. I’m due up again so I was thinking about that.
gpt
Tetanus is a disease that causes muscles to contract, and the vaccine contains just enough of the active substance to induce a slight but persistent (and luckily temporary) contraction at the site of injection. That's why the nurse or whomever is administering the vaccine asks which arm you want for the shot; it's generally easier to tolerate in the non-dominant arm.