The poor mice make a sound because they do not have the strength to fly.

This couplet charmingly points out a simple truth about mice: they make a lot of squeaky noise, but unlike birds, they don't possess the amazing ability to fly. It's a gentle observation about how some creatures might be quite vocal or busy, yet lack certain powerful capabilities. It reminds us that making a commotion doesn't always equate to having significant strength or freedom, like the freedom of flight. It's a whimsical way to notice the unique limitations and strengths of different beings in the world around us.