Jǐngquǎn xùnliànyuán yòng gǒushào fāchū zhǐlìng，gǒu hěn kuài jiù pǎo le huílái。

警犬训练员用狗哨发出指令，狗很快就跑了回来。

The police-dog trainer used a dog whistle to give a command, and the dog quickly ran back.