how do elves become orcs

Elf: *pauses, considering the question* Well, it's actually quite rare for an elf to become an orc, but it has happened. The process is a bit mysterious and involves some complex magical forces. It's thought that an elf who has been exposed to dark magic or has made a pact with a dark power may be transformed into an orc. However, it's not something that can be done intentionally or controlled by the elves themselves. Why do you ask?