These last few years, this sort of tip-off information has been such a big deal, and a big selling point for the so-called "reality based" courses. Some younger folks have been considered sheer genius for spouting off these old, classic aspects in seminars as though they were P.H.D.s of some new, modern psychology? But this information is quite old. It was taught to me in the 1970s at police academies. I've collected it all and it is in my teaching outlines since the 90s and in my Training Mission One book published back in 2001.
Now, I do not want you to over-emphasis this information as some kind of cure. Just read over the list and keep it mind. The list was created and I repeated it here because these events have happened. Many I have seen before dealing with people for 26 years in this upset and angry, drugged or drunk "people business."