How does one know which kamma-cetana and action is related to which kamma-vipaka being experienced?

For instance if I go to a forest and a dog bites me on my leg while there. How do I know whether: example 1: a) the dog biting me is my kamma-vipaka from my intentions and actions from the past or from a past life or b) the dog biting me is my kamma-vipaka for being in that forest ? example 2: I do something bad and something bad happens to me 2 days later. How do I know whether: c) The bad thing happening to me is related to the bad thing I did. or d) The bad thing happening is not related to the bad thing I did. ?