Thus in the magic deer’s disguise Márícha lured him to the prize, And seen a while, then lost to view, Far from his cot the hero drew. Still by the flying game deceived The hunter’s heart was wroth and grieved, And wearied with the fruitless chase He stayed him in a shady place.

In plain words: The deer is really the demon Maricha in disguise. He keeps appearing and vanishing so that Rama follows him far from his hut. Rama grows angry, upset and tired, and he rests in the shade.