Quite the conundrum

Well, I just went to the ladies room at work.

And there, in the stall I generally frequent (third one in...never, EVER use the first one; it is, statistically speaking, the one used most often and, in my opinion, the one most likely to give you crabs), I saw the strangest thing.

Behind the toilet was a big piece of lettuce.

Now. How the heck'd that get there????

Inquiring minds want to know.

Thoughts?