 In one experiment , when offered live fruit flies ( Drosophila virilis ) , salamanders choose the larger of 1 vs 2 and 2 vs 3 . Frogs can distinguish between low numbers ( 1 vs 2 , 2 vs 3 , but not 3 vs 4 ) and large numbers ( 3 vs 6 , 4 vs 8 , but not 4 vs 6 ) of prey . This is irrespective of other characteristics , i.e. surface area , volume , weight and movement , although discrimination among large numbers may be based on surface area . 
