I watched a video about testing smartphones by workers in a factory before it is officially put into box and packed. I found that when the worker was quickly and massively testing and swiping 8 phones at the same time, there was one phone which obviously showed lag or not responded as quickly as other phones among a few swipes. I am wondering when all phones are made in the same factory by the same way why there could be a few exceptions. Is it usually due to human error when the phone is assembled? Do you think Apple will have their guidelines for their factories to put away those problematic phones for further testing or will they just let them go into the market and let warranty handle the problem?