I think if its a bone, you're better off boiling it with water first to get the stock. Then adding the stock to the vegetable and lentils. That's what I remember seeing from my mum's cooking. I think you're meant to cook the bone for a long time, till it becomes soft and all bone marrow-y. Then drain the stock of all the bits and pieces. So you wouldn't want it in your veg and lentils. I think so ... I no soup expert though!!! good luck!