invisible mouse

I kid you not. This was what I saw when I was doing my glasshouse duties in the animal house the other day. There was indeed no living creature in sight. If there was, it was truly invisible.I am still wondering if this was:

A. A failed experiment, resulting in a dead rodent
B. A successful experiment in an invisibility experiment by the collaboration of my university and the NZ Military Force to infiltrate other continent's military defense
C. An attempt of a joke made by a sad, mad scientist

I wish I could take your bets on this but I myself am not too sure of what the answer is. Although I would most likely circle C.

Insight: I work at the university glasshouse where I water plants. I also look after animals involved in "research" but shhhh...its supposed to be a secret.