what is it and how and when do you know when to do it?
sry dont have enough posts to post in NLP section

Is a technique used to determine details about another person in order to convince them that you know more about them than they know about themsleves. You can use it right after an opener and in comfort.

Cold Reading can take many forms, from very basic observations of ones, body language, mannerisims, facial expressions, voice tonality, use of words, verbally descripbing themselves, dress sense, eye accessing cues (the corner fo their eyes they are looking in when they speak- see any NLP book for a diagram of which corner represents which) etc etc.

Police use it when interergating criminals- who have tried to hide their true intentions through lying- attempting to supress their body language and by attempting to throw off the police.
However eye accessing cues, body language and even micro twinges in their facial muscles (which even I couldn't read) give away their true intentions.

Cold reading is also used by con artists such as fortune tellers who claim to be pyschic (any NLPier will tell you this is bull crap- buy My Voice Will Go With You-Rose for any example of how Milton Erikson did his own "fortune telling")

A basic form of cold reading is making an assuptive claim about a woman. In fact if you buy the Professional Bachelor by Brett Tate it has an awesome section called profiling the mini skirts for each "Species of Female"