ls -l
[several files and directories listed]
mkdir dir
mv * dir
[long pause, disk thrashing, not good]
^C
ls -F
dir/
ls -l dir/
[moved files + dir/]
ls -l dir/dir/
[moved files + another dir/ !!!]

Bad news.  mv should complain about an "invalid arguement"
when trying to mv dir/ into dir/ and should not do it
recursively.