Step 1: Set your email account to auto-respond to a particular individual with simple yet thought-provoking questions.

Step 2: Ask that person one (or potentially two) legitimate questions to get the ball rolling.

Step 3: See how many emails it takes for him or her to figure it out.

For example (note, this was not done with an auto-responder, but i really dont think it made a difference):

Tue, Mar 24, 2009 at 3:53 PM rice: Make it to Germany?
Tue, Mar 24, 2009 at 7:14 PM L: YES FOO
Tue, Mar 24, 2009 at 7:15 PM rice: ping pong tomorrow?
Tue, Mar 24, 2009 at 7:22 PM L: I’m in Germany, [censored].
Tue, Mar 24, 2009 at 7:47 PM rice: wait…what?
Tue, Mar 24, 2009 at 7:48 PM L: did you read your first question?
Tue, Mar 24, 2009 at 7:59 PM rice: wha…?
Tue, Mar 24, 2009 at 7:59 PM L: ok dude. Are you in Bonn, Germany? Answer yes or no.
Tue, Mar 24, 2009 at 8:30 PM rice: ummm….wha…?
Tue, Mar 24, 2009 at 8:33 PM L:
You asked: Make it to Germany?
I said: YES [FOO]
then you proceeded to ask if i could play ping-pong tomorrow.
How, pray, are we going to play? via video conference or are you coming over?

Tue, Mar 24, 2009 at 10:28 PM rice: waah?
Tue, Mar 24, 2009 at 10:29 PM L: keep thinking we’re playing tomorrow.
Wed, Mar 25, 2009 at 8:24 AM rice: whhhhhaaaaa?

I deem this a success.