Matchlocks were primed, cartridges rammed home, and swords loosened in their sheaths. Was it the Tuaregs again across our path? But Mohammed, the keen-eyed, shouted joyfully— “The oasis, the oasis! I see the palm-trees.”
it shows the over excitement when they find the oasis
Inarticulate means not being able to speak or express clearly. In this case, Peter was inarticulate because he was angry when Mr. Dussel teases Peter about his cat which he loves very much. Not the same with Mr. Dussel who claims he is allergic to cats.