As with any fart or burp-like sound that we can produce, this one requires a very small air exit aperture, one that, as whatevs said, flaps a bit.
It also requires that air is pushed in and remains there until enough pressure is built up to overcome the tight seal.
Wetness of the area can aid in enhancing the seal.
One thing that's necessary is for air to go in. Remove piston almost to the tip, thrust in...repeat. In cars, there is an extra hole for air and another for fuel...
Now, why anyone would be concerned that they never do that is beyond my comprehension...
It also requires that air is pushed in and remains there until enough pressure is built up to overcome the tight seal.
Wetness of the area can aid in enhancing the seal.
One thing that's necessary is for air to go in. Remove piston almost to the tip, thrust in...repeat. In cars, there is an extra hole for air and another for fuel...
Now, why anyone would be concerned that they never do that is beyond my comprehension...