What happens when rsync is backing up volatile files?

[James Jones]

I'm sorry -- this is so tedious.  I know this question gets asked all
the time but I can't find the relevant e-mails.  So here goes with the
lazy approach.

What happens if a file changes as it is being copied by rsync?
Does rsync fallover or is the file simply corrupted in transfer?

Cheers and apologies,

James