to pluck, to gather in the fingers, to rub, to scrape off, horse exercise area
捋 centers on a hand action that draws things together or strips them away: plucking, gathering with the fingers, rubbing, or scraping off. The rare "horse exercise area" sense is an obscure extension, possibly from a similar action of grooming or managing horses.
捋 combines 扌 (hand) with 寽, a component that likely contributes both sound and the idea of grasping or stripping. The exact historical development of 寽 is uncertain.
The hand radical 扌 beside 寽 suggests fingers pulling or scraping. Picture a hand plucking leaves from a branch or rubbing a surface clean.
For ラツ, imagine a hand plucking a rat from a pile of gathered scraps: rat -> ラツ, and the hand strips it away.