Around 1950, researchers from the Technion Institute in Haifa (Israel) and from New York University tried to explain this effect scientifically. In fact, there are two phenomena that contribute to this effect: on the one hand, the Bernoulli equation is used to explain it, on the other hand, the adhesion between the liquid and the spout material is also important.
According to the Bernoulli explanation, the liquid is pressed against the inner edge of the spout when pouring out, because the pressure conditions at the end, the edge, change significantly; the surrounding air pressure pushes the liquid towards the spout. With the help of a suitable pot geometry (or a sufficiently high pouring speed) it can be avoided that the liquid reaches the spout and thus triggers the teapot effect. Laws of hydrodynamics (flow theory) describe this situation, the relevant ones are explained in the following sections.
Since adhesion also plays a role, the material of the spout or the type of liquid (water, alcohol or oil, for example) is also relevant for the occurrence of the teapot effect.
The Coandă effect is sometimes mentioned in this context, but it is rarely cited in the scientific literature and is therefore not precisely defined. Often several different phenomena seem to be mixed up in this one.