Thanks a lot for the comments. I agree the one button control has its downsides but I stuck with it for a few reasons including the slithering motion (glad you noticed it!). There's definitely room for improvement.
You have a good point about the state flickering back and forth. The way the mechanic works under the hood is by checking whether the snake is crossing four lines, north, south, east, and west, branching out from the center. If 3 out of 4 of the lines are crossed then the game tells you to catch your tail. The idea was to force the player to get long enough and then 'loop' around the entire level. I appreciate the feedback about the flickering though and have some ideas on how to improve it.
Also really glad you liked the tail catching visuals :) I actually repurposed the same particle effect that I used for the pickups, just tweaked some of the parameters and spawned the particle effect over the entire snake.