[thedoc (OP)]

Nancy Noll asked the Naked Scientists:
   My Adult English Language Acquisition class and I were at a train display at a local conservatory last week.  The display was interactive.  One of the activities was to place one's hand on the spot where the outline of a hand was, and, in doing so, the house in the train display would light up.  We all laid our hands on it and, sure enough, the house lit up, except for one woman.  When she laid her hand on this place, nothing happened, until I or someone else put our hand on top of hers.  Then it worked. 

One of the employees working there and an email to the team who put the display together said that they think the display works on magnetism.  Some info that may or may not be pertinent about the woman: she said she is anemic and her hands were very cold.  But if it was only that her hands were cold that caused this reaction, why would the display work while I put my hand on top of hers.  I mean immediately the house lit up and I was touching nothing but the top of her hand. 

Anyway, I'm no scientist and have looked around online for a possible answer.  Maybe you all can shed some light.

Thanks
What do you think?

[evan_au]

Can a person be magnetic?

Yes, carbon-based life like people do respond to magnetic fields - but only very slightly.
People are billions of times less magnetic than iron-based magnets or pins.
This makes it unlikely that the display would have been triggered by magnetism. 

However, with an incredibly strong magnetic field, research teams have been able to levitate frogs, strawberries and other organic materials.

No frogs were harmed in making this video! (Ok, maybe a little disoriented...)

But this is a magnet weighing several tonnes, and cooled hundreds of degrees below zero; this would be expensive, and a hazard to anyone viewing the trains with iron or other metals in their pockets or clothing.

Other Possibilities?
Did the nominated spot have metal? If so, the display may have been triggered by electrical resistance. Some people have very dry skin, and would not make good electrical contact if they pressed lightly.

Was the nominated spot glass or plastic (an electrical insulator)? If so, the display may be triggered by capacitance. Again, pressing lightly may not have produced enough capacitance to trigger the display.

It is possible that there could have been an infra-red light source and detector observing the relevant spot (like the clips they place on your finger in a hospital). A hand would reflect more IR. Perhaps anemia causes less IR reflection?

[Colin2B]

Nancy Noll asked the Naked Scientists:

... the team who put the display together said that they think the display works on magnetism....

I would be surprised if this is true. Most displays like this work by change of capacitance or the conductivity of the skin. Both of these depend on blood flow and sweat on the hand which are reduced by cold or sometimes circulatory illness. Placing another hand over will cause a change of capacitance.
Without knowing the exact type of sensor it is hard to be definitive.
It would be interesting to know whether the person has any circulatory problems, particularly those affecting peripheral circulation.