... wearing a nightshirt, armed with a bayonet, standing in front of a latrine.
Click for bigger if that will help you figure it out. Found at drakegoodman's Flickr photostream, via I've Had Dreams Like That, via Uncertain Times.
p.s. sorry about the grammar here, which makes it sound like the cat is wearing the nightshirt and is armed with the bayonet...
Addendum: Reposted from 2010 in response to the comment "Is'nt having "a cat on your head" a slang for having a hangover in German?"
Ich habe Deutsch nicht seit viertzig jahren studiert, but after some searching I found the word "katzenjammer" has this etymology -
1840–50; < German, equivalent to Katzen (plural of Katze cat ) + Jammer discomfort, Old High German jāmar (noun and adj.); compare yammer.- and is used to describe the effects of a hangover. So perhaps this soldier was trying to depict what his head felt like that morning?
Addendum #2: A hat tip to reader Gus Bryngelson for the comment "The Garde du Corps had a lion on their helmets, this is likely what was being hinted at."