Sometimes people wonder why babies always put things in their mouths. That's actually the best way for them to learn about the world around them. Your tongue and lips are the most sensitive parts of your body, far more so than your fingers. Try an experiment. Take an everyday object, maybe a pencil, and feel it very carefully with your fingers. Now feel it with your mouth (don't worry, it won't make you sick). Your lips and tongue can feel where the wood and lead meet, the ridges on the metal band next to the eraser, the difference in texture between the raw wood, painted wood and rubber tip. You can smell it and taste it too, even taste the different parts of the pencil. Look how much more information your senses got! Think how much more a baby learns about his environment when they feel, smell, and taste their world this way! All those distinctions are the building blocks of scientific thinking. So as long as it's safe, don't discourage your baby from exploring his environment instinctively.
And tell me, did you try the pencil experiment?