handful, pick up with fingers
揸 centers on grasping a small amount with the fingers: picking up a pinch or a handful of something.
揸 combines 扌 (hand) with 查, which likely contributes the sound and may relate to examining or picking. The exact historical development is uncertain.
The hand radical 扌 beside 查 suggests fingers examining and picking up a small amount, like a pinch or a handful.
For サ, imagine picking up a pinch of salt with your fingers: salt -> サ, and your hand 扌 grabs just a handful.