Which level of Snakebird has the giant octopus in the background

I hope this question isn't too "trivial" as it is definitely "trivia."

The game "Snakebird" on iOS, in one of the underwater levels, has a giant sea monster/octopus show up in the background animation from time to time. It's slightly unsettling when the giant evil eye peers in at you, a really nice touch.

I wanted to show a friend, but I couldn't remember which level it's on, and it only shows up once in a while making it difficult to find again.

The underwater levels are 7, 8, 9, 13, 14, 15, 16, 17, and 18.

Does anyone know which level I can find this on, and whether there is a "trigger" that causes it to show up or do I just have to wait?

(I remember when I was playing the level where it showed up, it showed up several times in the course of the 20 minutes or so I spent trying to solve the puzzle.)