Everyone needs this word in their personal lexicon: snirtle
Snirtle is both a noun and a verb.
Meaning: A soft, suppressed laugh, a soft snortle (itself a reduced snort) or shortened snigger.
A snort is greater than a snortle, which is greater than a snirtle.
A snirtle should not be confused with a snigger, which is more vigorous and lasts longer than a snirtle.