Inhaling Seagull is an exploitable two-panel image macro series featuring a photograph of a seagull leaning backwards followed by a picture of the seagull squawking forwards. The first image is captioned with the word "inhales" while the second image is typically captioned with verbose copypastas and song lyrics.
On July 12th, 2012, YouTuber Dimaniztlt uploaded footage of a seagull appearing to throw its head backwards and laugh (shown below). Within five years, the video gained over 181,000 views.
On September 3rd, 2017, Twitter  user @dioyasu tweeted a two-panel image of the seagull leaning back and a deep-fried image of the seagull with the caption "yamero." The tweet received more than 38,000 retweets and 66,000 likes as of November 2018 (shown below, left). That day, the same user tweeted the two-panel seagull image with the caption "inhales / BOI," referencing the *breath in* / Boi meme. The tweet received more than 1,000 retweets and 2,400 likes in a little over a year (shown below, right).
On September 10th, 2017, Redditor FallingTower uploaded the image captioned with a Game of Thrones reference to /r/freefolk (shown below, left). The following day, Redditor Fedock submitted a variation of the image referencing the "omae ma wou shindeiru" meme to /r/dankmemes (shown below, right).
On September 13th, the Woken Memes Facebook page posted the image captioned with lyrics from the song "Somebody Told Me" by The Killers (shown below, left). The same day, Imgur user mentaljake uploaded a similar variation featuring lyrics from the song "All Star" by Smash Mouth (shown below, right).
Shut Seagull refers to a screenshot from the Inhaling Seagull video where the seagull's mouth is shut and its neck is extended. A photoshopped-in "OK Hand Emoji" (👌) is holding the seagull's mouth shut, and the word "shut" is written at the bottom of the image (shown below).
The image slowly spread across Reddit as an image macro through several high-interaction posts and re-posts, as well as on Twitter as a reaction image (examples shown below).