One of my questions has just been bumped onto the front page by the Community bot:
What modification was made by the Community bot?
Every so often the Community user will bump old questions. Quoting from its user profile:
I do things like […] Randomly poke old unanswered questions every hour so they get some attention
The only “modification” this involves is to change the last modified time in the database, and attribute an empty edit to the user. It doesn’t make any substantive edits to these posts.