chuckle|chuckled|chuckles

看到小狗追逐自己的尾巴，他忍不住轻声笑了出来。

He couldn't help but ___chuckle when he saw the puppy chasing its own tail.

他在听到有趣的故事时轻笑。

He ___chuckled at the funny story.

听到这个有趣的故事，她忍不住发出几声轻笑。

She couldn't help but let out a few ___chuckles at the funny story.