他在每一次喂狗吃肉之前都会响一次铃，狗有肉吃就会流口水，久而久之，狗一听到铃声就知道有肉可吃，就会不自主地流下口水。
tā zài měi yīcì wèi gǒu chī ròu zhīqián dōu huì xiǎng yīcì líng ，gǒu yǒu ròu chī jiù huì liú kǒushuǐ ，jiǔérjiǔzhī ，gǒu yī tīngdào língshēng jiù zhīdào yǒu ròu kě chī ，jiù huì de liú xià kǒushuǐ 。
He rings the bell every time before feeding the dogs. The dogs drool when there's meat to eat. As time passed by, the dogs would know that there's meat to eat once they heard the bell, and they would drool involuntarily.