Once they are on their back its all over for them.
A fisher will knock a Quill Pig out of a tree and it is said they can run down a tree faster than a fall from said tree so they are doing their thing soon after the Pig hits the ground.
But like stated, it may have expired from some other reason and then its just lunch for the next passer-by.
Many people kill them to prevent tree damage. they can be a target of opertunity for young shooters.
For the message of the Cross is foolishness to those who are perishing, But to us who are being saved, It Is The Power Of God. 1Corinthians 1-18