Guinea continue to use tools that are virtually identical to hand axes to clear forest. "The term biface should be reserved for items from before the Würm II-III interstadial", although certain later objects could exceptionally be called bifaces. Hand axe does not relate to axe, which was overused in lithic typology to describe a wide variety of stone tools. At the time the use of such items was not understood. In the particular case of Palaeolithic hand axes the term axe is an inadequate description. Lionel Balout stated, "the term should be rejected as an erroneous interpretation of these objects that are not 'axes. Subsequent studies supported this idea, particularly those examining the signs of use. Materials Hand axes are mainly made of flint, but rhyolites, phonolites, quartzites and other coarse rocks were used as well. Obsidian, natural volcanic glass, shatters easily and was rarely used. Uses No academic consensus describes their use, but it is commonly agreed that the hand axe was some form of unhafted all-purpose tool. The pioneers of Palaeolithic tool studies first suggested that bifaces were used as axes despite the fact that they have a sharp border all around. Other uses seem to show that hand axes were a multi-functional tool, leading some to describe them as the "Acheulean Swiss Army knife". Other academics have suggested that the hand axe was simply a byproduct of being used as a core to make other tools, a weapon, or was perhaps used ritually. Wells proposed in 1899 that hand axes were used as missile weapons to hunt prey – an interpretation supported by Calvin, who suggested that some of the rounder specimens of Acheulean hand axes were used as hunting projectiles or as "killer frisbees" meant to be thrown at a herd of animals at a water hole so as to stun one of them. This assertion was inspired by findings from the Olorgesailie archaeological site in Kenya. Few specimens indicate hand axe hafting, and some are too large for that use. However, few hand axes show signs of heavy damage indicative of throwing, modern experiments have shown the technique to often result in flat-faced landings, and many modern scholars consider the “hurling” theory to be poorly conceived but so attractive that it has taken a life of its own. As hand axes can be recycled, resharpened and remade, they could have been used for varied tasks.