Let Birdie perch on your desk or shelf like a small bird on a branch. He'll help you open letters with his tail.
A paper knife is of course a tool used to open envelopes, but have you found yourself writing any letters lately? Letters are a form of old-fashioned "analog" communications, which can actually be really fun. The designer hopes that giving this "Birdie" as a present can help trigger that kind of communication for you.