英语达人，snigger和smirk有什么区别？

snigger：Laughter is an audible expression or appearance of merriment or amusement or an inward feeling of joy and pleasure (laughing on the inside). It may ensue (as a physiological reaction) from jokes, tickling and other stimuli. ...暗笑，窃笑
例如：
What are you sniggering at? Haven't you seen people kissing before?
你们笑什麽? 没见过接吻吗?
Her shabby appearance drew sniggers from the guests.
她样子寒酸, 客人不禁暗自发笑.

smirk：an affected, often offensively self-satisfied smile.
假笑，自得的笑，做作的，通常是自鸣得意、令人生厌的微笑
例如：
Come on, professor, do not smirk at me like that .
拜托！ 老师，你不要那样对着我假笑。
Wipe that smirk off your face!
别那么傻笑了!

前者是偷偷的笑，笑而不露；而后者是说傻笑，有点不雅。