Why does the Den Den Mushi look so much like their owner?
When a person calls or speaks through a Den Den Mushi, the Den Den Mushi will mimic the person's speech and display their emotions as well as take on the distinctive physical traits of the person on the other end. In other words they don't take the appearance of their owner but rather the one that is calling, and then return to normal once the call has been terminated. Think of it like adding a picture to your contacts to know who is calling.