Three prisoners of war were taken to a field and shown a box containing two white beenies three black beenies. The soldiers then blindfolded the POWs, placed a beenie on each of their heads and lined them up as follows before removing the blindfolds: 3-> 2-> 1-> (the arrows indicate the way each POW is facing) POW #3 could see both POW #1 and POW #2, POW #2 can see POW #1 and POW #1 can't see anybody. The POWs are not allowed to move and the first time one of them speaks he must correctly guess the color of his own beenie. If he is wrong, all the POWs will be killed on the spot, but if he is right all the POWs will be released. After a few minutes, POW #1 says, with absolute confidence, "I am wearing a black beenie" and the POWs are released. How did he know what color his beenie was? Again, if you already know this, don't say the answer.