In certain situations, copying files from the Mac file system to a different fs (e.g. to NTFS via NTFS-3g) results in the creation of extra 4KB-long files with names that begin with ._
Not sure how to prevent this. Look at the comments in this post.
To erase all those files from a directory tree:
$ rm */._* -R -v
(careful...)
Also see this for a terminal command that merges ._s with the original file
