Grip strengthening fun - Water shooter

I don’t know the proper name for this toy. I call it a water shooter.

It’s made of a hard styrofoam outer cover/plastic inner tubing. You pull up the green part (plunger) with one hand while gripping the blue part which is submerged in water. This motion sucks in the water into an inner plastic tube.

Then you push the green top (plunger) towards the lower blue part to shoot out the water (aiming at an object or person).

It’s simple, but oh so good for strengthening his fingers (grip) and engaging the upper arms.

At the moment, he still has much difficulty gripping it (both left and right hands) to draw in the water but can now push to shoot out the water. He finds it fun (when he shoots) despite the obvious frustration (I help him in drawing in water). Thanks for the gift, Fe!