by hedges » Oct 26th, '11, 09:14
Most likely scenario: if people are standing very close to you, you can tell which way they're facing when they speak, from the sound and other cues such as their breath touching you. Presumably you said something like "I'm looking at someone in the crowd", or otherwise somehow accidentally indicated that they should try to guess which way you're facing. Your head was oriented exactly towards the guy when you were describing him and you were standing very close to your volunteer. I think she was able to determine which way you were pointing using sound and your breath - and if you touched her, perhaps holding both of her shoulders or something, (you mention "strict control") you may have also accidentally indicated the direction by touch.
The great thing about this story is that the method was obvious to your volunteers but (despite suggestions like this one) it's still a total mystery to us! That's hilarious...!
I think this is a variation of "the learned pig" principle, where the animal is asked difficult multiple-choice questions and answers with snorts or hoof taps. Of course, the animal itself doesn't know the answer - it takes its cue from the trainer - who may even be unaware that they are indicating the correct answer by their own actions. The animal just needs to know that if it taps its hoof when the audience tension is at its highest (gasps, screams, leaning forward), or when the trainer raises his eyebrows and nods slightly, it gets a treat.