 Suppose that an event \(S\) is a sign of a cause \(C\) that produces an effect \(E\). For the probability of \(E\), knowing whether \(C\) holds makes superfluous knowing whether \(S\) holds. Observation of \(C\) screens off the evidence that \(S\) provides for \(E\). That is, \(P(E\mid C \amp S) = P(E\mid C)\). In Newcomb’s problem, assuming that the agent is rational, his beliefs and desires are a common cause of his choice and the prediction. So his choice is a sign of the prediction’s content. For the probability of a prediction of one-boxing, knowing one’s beliefs and desires makes superfluous knowing the choice that they yield. Knowledge of the common cause screens off evidence that the choice provides about the prediction. Hence, the probability of a prediction of one-boxing is constant with respect to one’s choice, and maximization of evidential expected-utility agrees with the principle of dominance. This defense of evidential decision theory is called the tickle defense because it assumes that an introspected condition screens off the correlation between choice and prediction.