First, it's a reference to [this classic meme](https://www.youtube.com/watch?v=d6gBu2Zd7Bc) (a four second video)
Second, it's a reference to how [Top Plush](https://www.deviantart.com/topplush) has the "marker test" where his pony plushes must be able to hold a marker between their butt cheeks… and when he made his latest Dash plush, he did it with a goddamn butcher's knife: 