It went through a five-and-a-half-minute period of ~25% CPU and "Not Responding"... and then finally came out the other end, but it's still chewing on moving a large number of files, slowly growing, back to 5.16GB in the time I've spent writing this.
There's Got To Be An Easier Way!™
(Yeah, boot off a recovery thumb-drive and nuke the whole damn folder from orbit.)