Download several movies (for ex. with limewire, mldonkey or some other p2p).
While downloading, open the folder that contains the partial files.
Nautilus creates the thumbnail for each file, but since these files are
constantly changing, it doesn't stop making new thumbnails. Cpu usage goes to
100% until you leave the directory and wait some seconds. Top shows
totem-video-thumbnailer working hard.
In nautilus preferences you can set "create thumbnails only for files smaller
than 10MB", but it keeps making thumbnails for bigger movies.
Disabling thumbnails at all for local files solves this, but a timeout should be
a better solution: when thumbnails for a given directory are created, don't
create new thumbnails for a while.