I think they took a picture of a vase, and created two derivative images of the vase, one which was more cat-like and one which was more truck-like. In both cases, participants did better than average at guessing which one was the derivative image. In any case, I don't think this is explained by the bobo-kiki effect, since they were able to get the subjects to select both inorganic (truck) and organic (cat) derivatives of the same source image.