Most music makes a point, some how or other, of taking contrasting sounds and playing with them. Melodies are no exception – pieces of music often have more than one characteristic melody, theme, pattern, or riff and some of the interest in the music comes from how these melodies interact with each other.
Taking this interaction between melodies and changing it, gives endless possibilities for creating new, interesting sounds.
Here are a couple of examples of what you could end up with...