It's possible that:
* It's a misspelling: Perhaps you meant "sniggered" (to laugh quietly or in a sneaky way)?
* It's a made-up word: It's perfectly fine to create new words! If you're thinking of a word that sounds like "sniggled", you could break it down into its potential parts and come up with a word that makes sense.
Can you provide more context? For example, where did you encounter the word "sniggled"?