adverb taking the 'to' particle, adverb
smoothly; swiftly; without resistance
Describes something sliding, slipping, or moving along smoothly and quickly, often with a sense of ease or lack of friction. Common with verbs like 滑る, 進む, 抜ける.
蛇が草むらをするすると滑っていった。
The snake slithered smoothly through the grass.
彼はするすると難
He solved the difficult problem swiftly and effortlessly.
Onomatopoeic/mimetic word; the exact origin is uncertain, but it likely imitates the sound or sensation of something sliding smoothly.