Why does r car rev up 3-4rpms when you put the clutch down?

When you put the clutch down in a manual transmission car, the engine is disengaged from the drivetrain, allowing it to rev freely without load. This can cause the RPMs to increase momentarily due to the engine's ability to accelerate without resistance from the wheels. Additionally, if the throttle is still open or if there's an issue with the idle control system, it can lead to higher RPMs when the clutch is disengaged.