ANIMAL signals are often ’multicomponent’(1-3), consisting of displays with several parts to allow exploitation of different senses, An example is the courtship display of the peacock, which combines dashing movements with a noisy, shimmering show of his train feathers(4). Yet the significance of multicomponent signalling is unknown. As a model multicomponent signalling system, we investigated the naming signals of toxic insects, which often combine pyrazine odours with conspicuous coloration such as yellow or red(5-7). Here we demonstrate, in prey choice experiments with birds, that pyrazine interacts with red and yellow to induce strong aversions to these aposematic colours that are not shown in the absence of the odour. Pyrazine is shown neither to be inherently aversive, nor to induce aversion to a non-aposematic colour, green. To our knowledge, this study provides the first evidence that the function of multicomponent signals can lie in hidden psychological responses produced by the interaction of their components.