Side Eye Dog, also known as Dog Giving Side Eye or Capping Dog, refers to a photograph of a dachshund dog looking sideways toward the camera with a suspicious look and squinted eyes, known as the side eye. The image of the sus dog was first posted to Reddit in April 2015 and became a popular reaction image in the following years, particularly on TikTok, where it is attached to videos and images of people exhibiting sus behavior.