Deception at Bridge is to make your opponent think and act on information that is not true. With smoke screens and mirrors, you, the consummate magician, trickster, swindler, will create an illusion. This illusion that is in the mind of your opponent will lead him down a particular logical path that will cause him to act in your behalf. As long as you follow suit if you can; and do not use body language or voice (or unnecessary hesitations) to convey information (false or true), deception is perfectly ethical 
and legal.
        As a Defender you stand a chance of fooling the one person you do not wish to fool - your partner. If this happens, along with disastrous results, your partner's usual controllable demeanor could elevate to the homicidal level. Do not discount a lightening bolt of wrath from the heavens burning the cards right out of your hand. If you are a Defender, mislead the Declarer, not your partner. Remember what Abraham Lincoln said: "you can fool some of the Declarers some of the time; but all of your partners at no time."  The ideal situation is to bamboozle Declarer constantly, and your partner never. Of course, if your partner is in no position to use your misinformation, it does not matter if he is fooled. Being fooled and not acting is the same as not being fooled.
        In example 1 below, West's opening lead against 3 NT is the 4 H. East would normally win with the A H and return the Q H. South hold ups but is forced to win the third round. By then East has no Hearts and cannot, by train, boat or bus, get to his partner's hand.
           1.    NORTH
   H 8 7 
H J 10 6 4 3 
  H A Q 5 
   H K 9 2

But if instead East makes the tricky, tricky play (that is twice as tricky as just plain tricky) of the Q H, then South must take the trick while he still has a chance. After all West has the A H (so a misled South thinks) and cannot afford to have Hearts led through him by East. And when East gets the lead, the A and 5 of Hearts will set the hand.