This is an improvised firearm used in the Philippines. We, the Filipino boys call it sumpak. It is especially common in remote villages where there are plenty of jungle with bamboo plants.
It consists of about a foot of bamboo branch open on both ends for “barrel” and a “trigger” made of 3 o 5 inches of same diameter but equipped with a sturdy and polished stick enough in length and thickness to go through the hole of the barrel. The “bullets” would be any soft material that could be plugged on the top end of the barrel then pushed through to the other end. Bullets could be wet paper, kapok flower buds, herb leaves, and unripe fruits of sapang (karrarawit in Ilocano; lubalob in Tagalog; scientific name: Bridelia stipularis).To operate, push one bullet towards the end of the barrel, then put another at the top end. When you push this second bullet, the air inside the barrel is compressed and pushes the other bullet out of the other end, creating a PLOK or other such popping sound. Innovations include putting a broken off 7-Up or Coke bottle neck to make the popping sound louder. Some have a hole on the side with which to push a succession of bullets, thus getting a semblance of rapid fire. It is fun playing longest-distance shooting or war games with this toy – some kids take too long chewing bits of paper for bullet; others take too long pounding the bullet to allow for tighter air and thus stronger shoot.

I used to make this bamboo pumpgun during my younger days and this is one of the reason why I enjoyed a lot my childhood days. 🙂