OS X: Can I track what files are being accessed on a disk?
You can use fs_usage to see all system calls related to filesystem activities. Output is quite large, so you probably need to redirect it to a file


Run sudo fs_usage &gt; fs.out in Terminal
Start Word and wait for the external drive to spin up
Switch to Terminal, press Ctrl-C and look through fs.out


You can also limit the output to certain processes, see the man page for details on that.