Hi Pilou, if I have understood correctly, the problem is not actually with the current model that he has attached there, the problem happens once things like the spikes are booleaned to the main body and filleted so they are all connected together as one object.

Once they are connected together into one object, it appears that SketchUp does not have any easy way to break them apart again into logical pieces. Most other polygon-based modelers would have a function to separate a mesh into different chunks where each chunk had polygons connected to each other through shared vertices, but SketchUp does not seem to have this.

But exporting to OBJ format and using that utility SeparateOBJ program I think should do the trick.

- Michael