What is an example of shifting the burden of proof?

Could you provide an instance where the burden of proof has been shifted in a real-world scenario? Imagine a situation where one party, let's say a prosecutor in a criminal case, initially has the responsibility to prove their allegations. However, due to certain circumstances, this responsibility is then shifted onto the defendant. Can you give a concrete example of such a situation, highlighting the specific reasons behind the shift and its implications for both parties involved?