$ edit (1)
$ git-update-index frotz.c filfre.c
$ mailx (2)
$ git reset (3)
$ git pull git://info.example.com/ nitfol (4)
(1) you are happily working on something, and find the changes
in these files are in good order. You do not want to see them
when you run "git diff", because you plan to work on other files
and changes with these files are distracting.
(2) somebody asks you to pull, and the changes sounds worthy of merging.
(3) however, you already dirtied the index (i.e. your index does
not match the HEAD commit). But you know the pull you are going
to make does not affect frotz.c nor filfre.c, so you revert the
index changes for these two files. Your changes in working tree
remain there.
(4) then you can pull and merge, leaving frotz.c and filfre.c
changes still in the working tree.