Quantitative metathesis is when we change the amount of sounds in a word to make it easier to say or hear. It's like when we play with Lego blocks and we can change their shape to make something new.
Let's say we have a word like "banana." That's a pretty long word, and it has three 'a' sounds. With quantitative metathesis, we can change the amount of sounds to make the word easier to say. So instead of saying "banana," we might say "bananner." That way, we only have to say two 'a' sounds.
Another example is the word "ask." Some people might say it like "ax," which is just one sound instead of two. That's another example of quantitative metathesis.
Overall, it's a way to change the sounds in a word to make it easier to say or hear.