How does git now about future renames during a rebase?

I had a history that looked like this:

1. some other commit
2. commit that moves files from one directory to a new directory
3. commit that edits files in the new directory.

I then did an interactive rebase to move the commit 3 before commit 2.

1. some other commit
3a. commit that edits files in the new directory.
2a. commit that moves files from one directory to a new directory

I didn't expect this to work, but somehow git worked out that it needed to apply the change in 3 to the original location of the files.

How does it do this?

jon.,