points on the body where acupuncture needles are used for abdominal or lower back problems. Evidence from the body suggests Ötzi had these conditions. This has been cited as evidence that practices similar to acupuncture may have been practised elsewhere in Eurasia during the early Bronze Age; however, The Oxford Handbook of the History of Medicine calls this theory "speculative". It is considered unlikely that acupuncture was practised before 2000 BC. Acupuncture may have been practised during the Neolithic era, near the end of the Stone Age, using sharpened stones called Bian shi. Many Chinese texts from later eras refer to sharp stones called "plen", which means "stone probe", that may have been used for acupuncture purposes. The ancient Chinese medical text, Huangdi Neijing, indicates that sharp stones were believed at-the-time to cure illnesses at or near the body's surface, perhaps because of the short depth a stone could penetrate. However, it is more likely that stones were used for other medical purposes, such as puncturing a growth to drain its pus. The Mawangdui texts, which are believed to be from the 2nd century BC, mention the use of pointed stones to open abscesses, and moxibustion, but not for acupuncture. It is also speculated that these stones may have been used for bloodletting, due to the ancient Chinese belief that illnesses were caused by demons within the body that could be killed or released. It is likely bloodletting was an antecedent to acupuncture. According to historians Lu Gwei-djen and Joseph Needham, there is substantial evidence that acupuncture may have begun around 600 BC. Some hieroglyphs and pictographs from that era suggests acupuncture and moxibustion were practised. However, historians Lu and Needham said it was unlikely a needle could be made out of the materials available in China during this time period. It is possible that bronze was used for early acupuncture needles. Tin, copper, gold and silver are also possibilities, though they are considered less likely, or to have been used in fewer cases. If acupuncture was practised during the Shang dynasty (1766 to 1122 BC), organic materials like thorns, sharpened bones, or bamboo may have been used. Once methods for producing steel were discovered, it would replace all other materials, since it could be used to create a very fine, but sturdy needles. Lu and Needham noted that all the ancient materials that could have been used for acupuncture