hm word question...are 2way mirrors the ones they use in copshows n supermarkets n ish? then this pencil thing is a neat trick to find out if theyre watchin you, huh. well last time i was interrogated for stealing alien technology from a secret underground base near berlin they took all my pencils away first tho. bummer.
Yes, two way mirrors you can see through from the other side and spy on people. You can use your finger to test the mirror if you hold it down at a 45 degree angle and touch the mirror. The reason it does this is because the reflective coating on a one way is on the backside of the glass and the space between the pencil/finger is the glass thickness. On a two way the reflective coating is on the front of the glass so there is no space between the pencil/finger. Try it on a mirror at home then do the same with a flat piece of chrome plating. You will see the difference.
In Germany in one city, there is a public toilet with two way mirror around, so that you can't look inside, but from inside you can see the people going around shopping. That's disgusting! I couldn't relax on this toilet.