I once paid a great deal of attention to card-sharping tricks and as I acquired them, either of myself or from practised gamblers, I demonstrated them to the young criminalists. For a long time I refused to believe what an old Greek told me: “The more foolish and obvious a trick is, the more certain it is; people never see anything.” The man was right. When I told my pupils expressly, “Now I am cheating,” I was able to make with safety a false coup, a false deal, etc. Nobody saw it. If only one has half a notion of directing the eyes to some other thing, a card may be laid on the lap, thrust into the sleeve, taken from the pocket, and God knows what else. Now who can say in such a case whether the sensory glance or the intellectual apprehension was unskilful or unpractised? According to some authorities the chief source of error is the senses, but whether something must not be attributed to that mysterious, inexplicable moment in which sensory perception becomes intellectual perception, nobody can say. My favorite demonstration of how surprisingly little people perceive is quite simple. I set a tray with a bottle of water and several glasses on the table, call express attention to what is about to occur, and pour a little water from the bottle into the glass. Then the stuff is taken away and the astonishing question asked what have I done? All the spectators reply immediately: you have poured water into a glass. Then I ask further with what hand did I do it? How many glasses were there? Where was the glass into which I poured the water? How much did I pour? How much water was there in the glass? Did I really pour or just pretend to? How full was the bottle? Was it certainly water and not, perhaps, wine? Was it not red wine? What did I do with my hand after pouring the water? How did I look when I did it? Did you not really see that I shut my eyes? Did you not really see that I stuck my tongue out? Was I pouring the water while I did it? Or before, or after? Did I wear a ring on my hand? Was my cuff visible? What was the position of my fingers while I held the glass? These questions may be multiplied. And it is as astonishing as amusing to see how little correctness there is in the answers, and how people quarrel about the answers, and what extraordinary things they say. Yet what do we require of witnesses who have to describe much more complicated matters to which their attention had not been previously called, and who have to make their answers, not immediately, but much later; and who, moreover, may, in the presence of the fact, have been overcome by fear, astonishment, terror, etc.! I find that probing even comparatively trained witnesses is rather too funny, and the conclusions drawn from what is so learned are rather too conscienceless.[194] Such introductions as: “But you will know,”--“Just recall this one,”--“You wouldn’t be so stupid as not to have observed whether,”--“But my dear woman, you have eyes,”--and whatever else may be