A slightly subtler characteristic is provocability . Players that chose to ignore a single defection or postponed retaliation for it were less successful. Not surprisingly, the other player often detected this unresponsiveness and continued to defect. As a result, neither player emerged from the match with a good score. Wants to win cooperates on the first round, but thereafter does the opposite of whatever the other player did in the previous round.
Random player tosses a coin on each round to choose randomly between cooperation and defection.
2B4 defects on the first round, cooperates in the second round, and thereafter does whatever the other player did two rounds earlier. The Sabrina player cooperates on the first two rounds and alternates between cooperation and defection thereafter. The Whoever player cooperates on the first two rounds. If the other player's previous two moves comprise one cooperation and one defection, however, Whoever chooses randomly and with equal probability between cooperation and defection. Easily irritable cooperates for the first five rounds.