Instead of trying to trick your actors into doing what you what them to do by means of some exercise (without explaining the purpose of the exercise) why not just give them the note?
The actor/director relationship is one that has to be based in trust. If you have a long history of working with someone, you can skip to whatever the shorthand formula between the two of you is - do this exercise here, insert this tool over there. However, if you're new to an actor and you try to skip over the "getting to know you phase" and go directly to "I'm going to get you to do exactly what I want you to do", I start to feel manipulated. And defensive. Which isn't where any of us do our best work. I begin to sense that you want something from me but you're not telling me what that something is. Trying to figure out how to deliver what someone wants is hard enough when they tell you what they want. It feels near to impossible when they don't tell you.
Sharing is great. It's amazing when you can pool the brilliance and experience of all the minds on your team to crack open the story. However, springing an exercise on your actors by saying "this is what we're going to do today" isn't sharing. It's dictating. And explaining why you dictated something after you've dictated it, doesn't mean you didn't dictate it. It means you want people to excuse your dictating because you think it was such a good idea. And it might be a GREAT idea. But I'm much more likely to feel like I've been shoved around and I can't have a open conversation with you.
Time is always short in any rehearsal process. And your shortcut may well be the fastest way to get to your desired result. But the fastest solution isn't often the most lasting solution. Taking the time to build solid, respectful relationships will have a significantly greater payout in the long-term.
Give the note. Give up a little bit of control. Recognize that we both
have training and tools and tricks. We're both creative. We're both
problem solvers. At the end of the process, I'm the one who has to
embody the choices we've made. If I can get there in a way that I'm
comfortable with, in a way that makes sense to me, that's an excellent
solution for both of us - you have what you envisioned and I feel
valuable for being able to give it to you (and I feel comfortable doing
it). Value the way I might add to the process. If I get stuck, then,
please, by all means, offer up your exercise and together we can figure
Or at least have the conversation. Beforehand. It doesn't have to be
long and involved. It can be as simple as "Hey, I'm looking to get more
of a feel for such and such in this scene. Would you mind if we tried
this to see if we can find more of that?"There's nothing worse than not having any idea why you're doing an exercise. Will some people fall into what you want them to discover? Sure. But monkey's with typewriters will eventually make words. Rather that leaving it up to fate, why not just fill everyone in on what it's all about and let everyone get as much as they possibly can out of it.