As soon as the birds stroke them with stones, they became like eaten straw. Observe this event which happened by a super power that is over the human beings’ ability.

كَعَصْفٍ (straw): It is the hay that animals eat and trample on, or it is the dry fallen crumbled leaves. This same word comes in other verses as a description to strong wind:

 ﴾جَاءَتْهَا رِيحٌ عَاصِفٌ ﴿

 (there comes a storm wind.) (Al-Anfal: 30)