What is the definition of Sniggers?

Here's a short, funny rhyme incorporating “sniggers”: “To emit a snigger – a tiny, glee-filled sound, Like a badger judging socks upon the ground. My aunt Mildred, with spectacles askew, Just 💎sniggers💎 at my hat; it’s utterly blue!”

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Just 💎sniggers💎 at my hat; it’s utterly blue!”