The focus is on objects - not everything you do on stage should be verbal. In fact, there should be quite a lot you do on stage that isn't verbal, and in some cases is completely non-verbal. Putting a pipe in your mouth during the scene lets you think about what's happening and what's going to happen - what your character, the pipe-smoker, is going to do next, what he/she is going to say, how he/she is going to react to what your fellow player just said or is saying, and so on.
The next you rehearse a scene, try this - spend the first 30 seconds saying absolutely nothing. Instead, interact with the objects that are the world of the scene - which means that, most likely, you'll have to create them in the first place. If your scene is in a kitchen, don't just barge in and ask "Hey, mom! What's for dinner?" Spend some time watching (silently) your scene partner cooking, check out the refrigerator, the pantry, the cupboard, the place where you keep your secret stash of cookies and discover you finished them the last time you checked there, find a piece of gum and chew it for a while, sit down at the kitchen table and drum your pencil impatiently... there's lots you can do without saying a word. Each of those actions lends some tidbit to your character, the location, your relationship with your scene partner, and so on.
If you don't talk, it gives you more time to hear those tidbits.