I'm sure you have already seen the white frothy and gas bubbles that forms in the beer when you poor it to a glass. However, do you know the science beyond that? Maybe you already knew that beer is a supersaturated solution of carbon dioxide (CO₂) because it has more gas than it should. When beer is inside the bottle, the CO₂ is in equilibrium because the bottle is pressurized. When you open the bottle, the pressure decreases and the CO₂ comes out and makes a special noise: Xuhaa!
After, when you pore the beer to the glass, part of the excess gas comes out of the liquid and drags some liquid with it, forming frothy in the solution top. This happens due to the energy that you add to the supersaturated liquid when you make it flow, some fissures in the glass and impurities. If you let the beer, the frothy will start to disappear and small bobbles continue to flow up through some nucleation points (glass fissures). This because gas bubbles in the beer don't form spontaneously and need some special points of nucleation to grow. That's why when you had some salt to the beer it starts a huge formation of bubbles due to the higher number of nucleation points that enable the formation of gas bubbles. Science is wonderful? Try it and discover science at home!