Warfare between tribes was common, generally over land conflicts or to restore mana. Fighting was carried out between subtribes (hapū). Although not practised during times of peace, Māori would sometimes eat their conquered enemies.[69] As Māori continued in geographic isolation, performing arts such as the haka developed from their Polynesian roots, as did carving and weaving. Regional dialects arose, with differences in vocabulary and in the pronunciation of some words. In 1819 two young northern chiefs, Tuai and Titere,[70] who had learnt to speak and write English, went to London, where they met the language expert Samuel Lee. They stayed with a school teacher, Hall, who they told that even in Northern New Zealand there were "different languages and dialects".[71] The language retained enough similarities to other Eastern Polynesian languages, to the point where a Tahitian chief on James Cook's first voyage in the region acted as an interpreter between Māori and the crew of the Endeavour.