seize a shackle, mouse a hook
 

The Mate and I are having a discussion. My Navy training taught that you seize a shackle and mouse a hook. The mate believes that you mouse a shackle, and seize turnbuckles and other standing rigging.
I told him I would defer to Ashley's BOK, but we don't have one aboard, so in lieu of that I will defer to the group here.

BTW he is an old Pt Townsend hand who recently swallowed the anchor and sold his boat. I will be hauling the Jack a Hearts out in PT on June 16th..

Both actions are mousing. The confusion may arise because it's best practice to use siezing wire to mouse a shackle.