OK Pertex, thank you for the explanations ! I thought that was quite impossible too... Anyway, I have found a way to link each of my object to (at least) two verbs, so that the sub-menu will always be useful
And you're right, objects with just one interaction aren't so user-friendly, so I will change my mind and my game should be more complex and interesting now.
And... by the way... May I ask you another question ?
I'm using the "showpicture" script, but is it possible to tweak it to center the displayed picture ? I've tried an expression like "<align align=\"center\">"picture.jpg"</align>" (that's the one used in the "print centered message" script), but it returns an error message... Why am I so bad with scripts ?