The researchers delivered short electrical pulses to either the upper left canine tooth (the pointy one) or the lower left canine tooth in the subjects.

科研人员给上颚的左犬齿（比较尖的那颗）或者是下颚的左犬齿注射一个短的电脉冲。

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The training to open their mouths was key to staff spotting a rotting upper left canine bothering Arktos last year and a damaged tooth that troubled Walker in 2011.

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