Definition of "sniggling"

How little Tim and Jim stood hiding behind doors, peeping out surreptitiously with gigglings and snigglings indescribable, whilst the august visitor laboriously ascended the narrow and tortuous “nursery staircase,” has passed into the annals […]

1887, Mrs. H. Lovett Cameron, Pure Gold, page 257

The loud whispers and devious snigglings were still ringing in her ears, long after they had been well on their way. She hadn't bothered to make friends with any of them, in that her way of living wasn't what they might call respectful; […]

1984, Freddie O. Durant, The Donaldson Mansion, page 151