The Alien

 was the twist of Big Brother 3. The Alien was to wreak havoc on the houseguests by pretending to be a real houseguest, playing alongside the other fifteen, by causing paranoia or physically sabotaging the game. The Alien would be granted $50,000 if he or she made it to the half-way point in the game, five weeks, undetected. The only way to rid the house of The Alien was for them to be exterminated, in which they had to be sitting on the block come eviction night. The eviction would not take place, leaving the other nominee safe, and The Alien banished. Should they make the Jury stage, The Alien would not vote for a winner.