a simple text or a message written below to your YouTube shorts giving an idea about the uploaded YouTube shorts video to the viewers
Yes, copying another YouTube video's description can be considered reused content by YouTube
Some examples of video descriptions for animal videos I have seen on Twitter include:

An African penguin walking outside its enclosure approaches a beluga whale tank and watches the beluga swim in front of them as the beluga smiles and makes excited facial expressions
A museum volunteer shows off an amelanistic striped corn snake with vertical dark orange and light orange stripes and a yellow body that is about one meter long. The snake looks at the camera with its red eyes and sticks out its tongue several times