I saw it on Thursday indeed. It's the rat seen on the OP webpage with "Exit at the gift shop", if I remember correctly.
Found right here, above Amnesia actually: http://maps.google.com/maps?f=q&source=s_q&hl=en&...
Found right here, above Amnesia actually: http://maps.google.com/maps?f=q&source=s_q&hl=en&...
http://www.flickr.com/photos/troyholden/4544878324/
Although the rat has apparently been spotted in SOMA.