system
Given the following post, respond as if you're commenting on Reddit:
human
[Mario] Why do Bullet Bills have arms and teeth? What's their life like, in general?

Do they live for just one shot and then die?
gpt
Most likely they are automatons with some limited intelligence. Most Bullet Bills actually do not appear to have mouths; only arms and eyes, both of which would be useful for steering. The mouth, when it does appear, seems to exist for intimidation only. 

We only ever see Bullet Bills fired from cannons and they self destruct shortly after if they don't hit anything, so there is no evidence of them having any kind of natural life cycle.