Egg white and milk have viscosity and surface tension.

When stirred for a long time, the boundary between the air and the two will be similar

Due to the effect of "fusion" -

We can often see the scene of air turning into small groups mixed with egg whites and milk in life,

and when "foaming" the air It will turn into finer bubbles mixed in.

Because of surface tension——

Note that when foaming, the area of ??egg white and milk at the edge of the bubble becomes the "surface".

So, these two ingredients will turn into paste due to surface tension.

In cooking, it is called physical foaming