Electroencephalographic data suggest that spoken words produce an enhanced output of the brain's automatic deviance detection system, as reflected by the mismatch negativity. Using meaningful and nonmeaningful whistles, we sought to distinguish the effect of semantic content on the brain's deviance detection system from language-specific stimulus features. In the meaningful condition, study participants heard a human 'wolf whistle', which is commonly interpreted as an unsolicited expression of sexual attention. In the nonmeaningful condition participants heard an acoustically identical, but digitally rearranged, version of the wolf whistle. The mismatch negativity amplitude was significantly larger when the infrequent stimulus was meaningful than when it was meaningless. These data suggest that enhanced mismatch negativity magnitude was due to the semantic valence of the eliciting deviant.