Final answer:
When trimming a bird's nails, you should stop when the cuticle of the nail turns clear or translucent.
Step-by-step explanation:
While trimming a bird's nails, you should stop when the cuticle of the nail turns clear or translucent. The cuticle is a layer of dead epithelial cells that covers the edge of the nail plate and helps to seal the edges to prevent infection. As you trim the nail, if you continue cutting after reaching the clear or translucent area, you may cause bleeding and discomfort for the bird.