Now you will have to go back to Mustapha. I assume that you remember where to find him (he's standing next to the camels). Start the conversation and choose some of the available topics from the list - 'What is going on?' and 'The Blood Rocks'. You'll find out that Mustapha will provide you with one of his camels, as long as you'll be able to heal the sick animal. Mustapha will advise you to meet up with one of the local healers, because he might be in possession of a remedy.
Thankfully, you won't have to spend a lot of time trying to find the healer. Click on a passageway located to the left of Mustapha. Once you're there, start moving towards the bottom of the screen and talk to an old man wearing a white robe (screen). Choose two topics from the list - 'Take care of the camels' and 'The Blood Rocks'. The old man will provide you with a remedy, but first you must find the source of the poison. You can't perform any other activities here, so go back to Mustapha right away.
You don't have to talk to Mustapha again, because you haven't obtained any new information since the last time you've spoken to him. Pick up a Fork and choose it from your inventory right away. Use the fork to collect some Curious plants. The plants can be found in front of the camels. Go back to the healer and show him the plants. Ask the old man to give you a remedy for one of the camels. As a result, you will receive Medicine for camels. Return to Mustapha and talk to him about your new findings. You are going to be transported to the tomb.