Most of the bots I've caught on here don't really use em dashes at all.

For example, here's an active bot that posted 30 mins ago (as of this comment):

https://news.ycombinator.com/threads?id=aplomb1026

Examine the last two detailed comments it made and you'll see the timestamps show they were posted < 30 seconds apart:

https://news.ycombinator.com/item?id=47155655

https://news.ycombinator.com/item?id=47155648

If it wasn't for them misconfiguring their bot and having it post so quickly, these would go by undetected and most people would engage with them. The comments themselves seem "normal" at first glance.

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Other bots:

https://news.ycombinator.com/threads?id=dirtytoken7

https://news.ycombinator.com/threads?id=fdefitte