A simple straw piston can be made of some common materials. Here is a possible way:

Materials:

plastic straw

A cotton ball

Stick or toothpick.

Some tape.

Some scissors

Steps:

At one end of the straw, cut a small hole with scissors, which is slightly larger in diameter than the stick or toothpick you use.

Pinch the cotton ball into a small ball and stuff it into the other end of the straw.

Insert a stick or toothpick into the hole of the straw until it touches the cotton ball, and then stop.

Seal one end of the straw with adhesive tape to prevent the cotton ball from falling.

Gently squeeze the other end of the straw until the cotton ball squeezes the other end of the straw. This process is similar to the process of compressing the piston when using an injector.

In this way, you make a simple straw piston. When you want to eject the toothpick, just insert the toothpick into the hole of the straw, and then compress the air at the other end of the straw to eject the toothpick. Note that this piston is not very accurate and may need to be adjusted repeatedly to achieve the desired effect.