Could anybody explain in more detail?
As for the immersion blender, intuition should tell you that the same principle should/or at the very least… might apply. Now it could very well not apply (but I'm quite confident that it does). To really prove if it does or not, one would have to do the rigorous math involved, which would include deriving the stream function for the flow situation, verifying if conditions allow for applying Bernoulli's principle, then applying the principle and verifying if it matches experimental observations... This is would be non-trivial to do (judging simply by the geometries involved) so I'm not even going to attempt do this…
However, I’ll try explaining the gist of the idea:
Bernoulli’s principle basically states that, within a flow of constant energy, when a fluid speeds up, it is corresponded with a drop in pressure and vice versa. Now looking at the immersion blender, intuition (and essentially conservation of mass) suggests that the fluid should be moving fastest between the edges of the blender/blade and the boundaries of the container/cup (i.e. areas where there’s very little space near the moving blender parts). Outside these regions, intuition would suggest the fluid is moving relatively slowly (e.g. near the top of the water level in the container cup). Since the fluid appears to move, and likely cross these regions (i.e. undergoes speeding up/slowing down), Bernoulli’s principle states that we should expect to see a pressure differential between these regions, where faster moving water regions should be at a lower pressure (i.e. acting as a vacuum / suction cup).
But again, whether or not this idea is true and is valid would have to be mathematically and experimentally verified…
