Why does a rotating drum apply a normal force on a body that's rotating inside it

A drum is rotating uniformly and on its inner side a body is rotating with it as well.

I know by applying newtons law, a normal force has to exist and I can calculate that but my question is why should it exist? I cannot visualise the body pushing radially outward on the drum which leads to the normal force.

Let’s focus on the element which is in contact with the body. Both of them have the same tangential speed . And for an instant they will move in unison without the body pushing radialy out. Then how does a normal force exist.

I’d be glad if someone pointed out.
Thank you