The description of their sleep
If one comes near them, he will be filled with fear, and will mostly run away from that scene. You deem them awake, while in fact they were sleeping. So that God filled the cave with desolation and terror.
As in the Quran 18: 18
وَتَحْسَبُهُمْ أَيْقَاظًا وَهُمْ رُقُودٌ وَنُقَلِّبُهُمْ ذَاتَ الْيَمِينِ وَذَاتَ الشِّمَالِ وَكَلْبُهُم بَاسِطٌ ذِرَاعَيْهِ بِالْوَصِيدِ لَوِ اطَّلَعْتَ عَلَيْهِمْ لَوَلَّيْتَ مِنْهُمْ فِرَارًا وَلَمُلِئْتَ مِنْهُمْ رُعْبًا
The explanation:
(And you [man] would have deemed them waking while they were asleep;
We turned them [once] to the right and [once] to the left;
whereas their dog was outstretching his two fore-legs on the threshold [of the closed gate.]
If you [man] had observed them closely, you would have turned back in flight and been filled – of them – with terror.)
2- The second feature mentioned in the aya is that God made them turn to the right once and to the left another time; so that their skin will not ulcerated with sores.
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The description of the cave
The gate of the cave was facing the north, so that the sun when it rises from the east, it will leave their cave going to the right, and when it sets, it depart from them to the left; while they were in the space of that cave.
As in the Quran 18: 17
وَتَرَى الشَّمْسَ إِذَا طَلَعَت تَّزَاوَرُ عَن كَهْفِهِمْ ذَاتَ الْيَمِينِ وَإِذَا غَرَبَت تَّقْرِضُهُمْ ذَاتَ الشِّمَالِ وَهُمْ فِي فَجْوَةٍ مِّنْهُ
The explanation:
(And you [man] would have seen the sun, when it would rise, going aside to the right away from their cave; and, when it would set, leaving them away on the left hand, while they were [asleep] in a broad space of [the cave.] )
It means: the sun rays did not touch them directly.
It means the gate of the cave faced the north.