Their approach hinges on the fact that similes exploit stereotypes to draw out the salient properties of a target, thereby allowing rich descriptions of those stereotypes to be easily acquired, e.g., that snowflakes are pure and unique, acrobats are agile and nimble, knifes are sharp and dangerous, viruses are malicious and infectious, and so on.
because they find that almost 15% of their web-harvested sim-iles are ironic (e.g., "as subtle as a rock", "as bulletproof as a sponge-cake", etc.