听到他蹩脚的模仿，几个男孩忍不住偷偷讥笑。

A few boys couldn't help ___sniggering at his clumsy imitation.

看到老师滑稽的打扮，几个学生忍不住偷偷发出了嗤笑。

A few students couldn't help but let out quiet ___sniggers at the teacher's funny outfit.