Octal 31 = 3 x 8^1^ + 1 x 8^0^ = 24 + 1 = Decimal 25

• The Yuki language in California has an octal system because the speakers count using the spaces between their fingers rather than the fingers themselves.[2]
• The Pamean languages in Mexico also have an octal system, because some of their speakers "count the knuckles of the closed fist for each hand (excluding the thumb), so that two hands equals eight."[3] https://en.wikipedia.org/wiki/Octal