first clue
in matters where a few outcomes are possible ,(like good/bad, yes'no ) it is easy through facial expression to transmit thoughts
proof
faces of people on american idol after they finish the interview and come out, even without seeing the pink slip, its obvious from looking at their faces whether they are going to hollywood or not.
second clue: how whole ideas can be turned into a matter of yes/no
consider this story :
there is no lectricity , i try a gaslamp but it doesnt have any gas , i go out to get some gas but i dont find any.
hence i stay in the dark.
if a stranger sees me he will have no idea as to why that is, there are an infinite number of possible explanations.( i am angry, retarded, photophobic? or maybe the stranger suddenly got blind etc etc)
but if my wife sees me , because she knows
a- i dont like to stay in the dark
b- if the electricity is out, we have a gas lamp
c-if the gaslamp had any gas in it , i would have lit it.
d-if the gas lamp didnt have any gas in it, i would have gone out for some gas.
e- if im in the dark, i must have not found any gas at the store or whatever.
so my wife, just by seeing me ,gets all this information without me saying a word(isnt that what they call telepathy?)
another example
two young people look at each other , they get an idea what the other perso's impression is .
how?
because they both share the quality of being young (hence with sex on their mind)
if the other person approved of them they would smile or approach them, this not happening one can deduce that the other person doesnt feel attracted to them.
so in a nutshell , telepathy is scientifically possible when the amount of shared background information make it possible to transmit complex ideas through expressions that signify simple ideas like yes/no or good/bad .
i think this is a good question because it gave me the opportunity to share my theory which i use mostly to explain to myself the apparent ability in animals to transmit ideas to one another non-verbally.