/usr/share/applications/screensavers/extrusion.desktop is in xscreensaver-gl-extra 5.30-1+deb8u2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | [Desktop Entry]
Name=Extrusion
Exec=/usr/lib/xscreensaver/extrusion -root
TryExec=/usr/lib/xscreensaver/extrusion
Comment=Draws various rotating extruded shapes that twist around, lengthen, and turn inside out. Written by Linas Vepstas, David Konerding, and Jamie Zawinski.
StartupNotify=false
Terminal=false
Type=Application
Categories=Screensaver;
OnlyShowIn=GNOME;
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