A dissection fallacy discovered by Dudeney (1958). The same set of tangram pieces can apparently produce two different figures, one of which is a proper subset of the other. This seems true only at a first glance: in reality the area is the same in both cases, since in the left picture the missing foot is compensated by a larger body.
See alsoDissection Fallacy, Tangram
This entry contributed by Margherita Barile