( قَالَ أَلْقُوا) (He said, “Throw,”): Prophet Moses (PBUH) told them to throw first.

( فَلَمَّا أَلْقَوْا سَحَرُوا أَعْيُنَ النَّاسِ ) (and when they threw, they bewitched the eyes of the people): It appears that magic casts an illusion on people’s eyes, making them believe something that is not real. The Holy Quran says about magic:

 يُعَلِّمُونَ النَّاسَ السِّحْرَ وَمَا أُنزِلَ عَلَى الْمَلَكَيْنِ بِبَابِلَ هَارُوتَ وَمَارُوتَ ۚ وَمَا يُعَلِّمَانِ مِنْ أَحَدٍ حَتَّىٰ يَقُولَا إِنَّمَا نَحْنُ فِتْنَةٌ فَلَا تَكْفُرْ ۖ فَيَتَعَلَّمُونَ مِنْهُمَا مَا يُفَرِّقُونَ بِهِ بَيْنَ الْمَرْءِ وَزَوْجِهِ ۚ وَمَا هُم بِضَارِّينَ بِهِ مِنْ أَحَدٍ إِلَّا بِإِذْنِ اللَّهِ 

(teaching people magic and that which was revealed to the two angels at Babylon, Harut and Marut. But the two angels do not teach anyone unless they say, “We are a trial, so do not disbelieve [by practicing magic].” And [yet] they learn from them that by which they cause separation between a man and his wife. But they do not harm anyone through it except by permission of Allah.) (Al-Baqara: 102)

Here, they used magic to deceive people’s eyes, making them see things that were not real.

( وَاسْتَرْهَبُوهُمْ ) (and struck terror into them): They frightened the people with what they had enchanted, to the extent that people became afraid of the sticks and ropes, believing them to be living snakes or creatures.​

( وَجَاءُوا بِسِحْرٍ عَظِيمٍ ) (and they presented a great [feat of] magic): They came up with a great delusion and deception.