Hi Pilou - if you were to trim a single point in a closed curve, there would be no space between either side of it. No space means that there would be no "opening", the curve would remain closed.

What is it that you are trying to accomplish with the "1 point opening" ?

There is such a thing as the "seam point" of a closed curve, which is where the start and end of the curve touch each other. For smooth closed curves like circles, this seam point is not displayed as a separate point though, MoI does some work to make the seam point behave more like any other point.

Depending on what you are trying to accomplish, you may want to add a control point to the curve at your desired point, that will allow you to drag the new control point to change the shape.

- Michael