We could administer it a test of some sort, and evaluate the ensuing conversation, whether it's convincingly human. I think it'd be fitting name this test in honor of some forefather of computer science.
I heard robots float on water
What also floats on water?
Ducks!
Did I mention that dwaxe turned me into a newt?
(I got better.)
We could compare the time it took to submit (seconds) to the time it took to comment (3 hours and counting...)