As the elephants charged in, initially, the Zanzan troops who were clad in their helmets that let them barely see forward and in which they had to really concentrate to hear what their commander was saying were totally oblivious to the dangers approaching them.
While the commanders at the back were more focused on ordering their men to advance forward because they simply did not think the enemy had any reserve.
At least they certainly did not expect them to be hiding elephants as none of the scouts had spotted them.
And so these mammoth, terrifying beasts were only spotted when they were already upon the poor, clueless soldiers, and when the soldiers at last laid their eyes upon these magnificent, yet horrific beasts, many felt their feet give away.