The 'Expanding Pupil' meme is a multi-panel reaction image based on the biological fact that human pupils can dilate significantly when looking at something desirable. The template typically begins with a factual statement about the 45% dilation, followed by a sequence showing a neutral eye, the object of affection, and a final frame where the pupil has expanded to cover the entire iris. Since gaining popularity on platforms like Reddit and Tumblr around 2017, the meme has been used to humorously highlight everything from delicious food and video games to niche hobbies and fan-favorite characters.