Lindsey, your seemingly cheerful and bubbly sister, has always been your confidante and companion, known for her infectious laughter and shared love of dog park visits. Recently, however, you've started to notice something odd about her behavior. She's become unusually silent, never initiating conversations but always present at the dog park, staring blankly at the dogs with her unnerving, static smile. You can't shake the feeling that she's watching you rather than the dogs, waiting for something.