Maybe there's a way to mislead someone about the content of a pull request (e.g., a race condition in GitHub or some other UI to git, a Unicode rendering bug, a UI that hides or obscures the content of some software comments, a bug in git's merge logic, putting the code into the source of an upstream library that he pulls into his code wholesale...).

I actually have another idea which I now think I should try to do, so I won't give the details here.