Other research suggests that the Piraha use a relative estimation system. Two options are few/many and more/less than I expected. The current belief in the literature is that more/less is the most accurate. I was fortunate enough to hear Prof. Gibson talk at Swarthmore College several months ago, and he seemed unsure of exactly how the Piraha use number. He was, however, quite sure that the convention (that they don't have any concept of number) was incorrect.