Maybe the Joker was putting his own mental instabilities on Samara; mostly he just assumed that every doctor was a threat. He couldn't see anything particularly foreboding about the man she pointed out, but then again, it didn't matter to him. With a few quick moves around a man screaming about fireants or something - who cared? - he grabbed the orderly by the back of the neck and dragged him 'round to face him.

"What did the lobster say to the chef?" He didn't give the man a second to even contemplate the joke, which had a pretty obvious punchline, really, just yanked a knife out of a pocket and flipped it open, stabbing it through the man's cheek.

When he started howling, the Joker giggled. "So, you know the joke, then?"