HOW כפרות PROTECTS FROM DEATH?

We find in the גמרא the concept of confusing the Satan
(כדי לערבב השטן). We also find a similar case of שינוי השם, 
changing the name of a חולה. (sick person)

The original מנהג of כפרות was also the same idea. It
was done for the protection of the children if there 
was ח"ו a גזירה for the זרע (child)  to die we confuse the 
שטן with a different זרע (seed) the bean plant which
gets thrown in the river.

At a later stage when the מנהג כפרות started for adults,
they wouldn't use the flower pot with bean זרע.
They used a גבר (chicken) instead to confuse the שטן
so not the גבר the man will die, but the גבר the chicken.

אמבצי