How to.
Requires no tape or cutting, just feed the left side into the flap and it will be secure enough with a good crease. But you could use double sided tape inside the flap if it really keeps you up at night.
You could doodle on it and turn it into a hungry shark, blooming flower or vagina dentata if you think that’d be funny. Embellish with tape or stickers. Go over the top with scalloped scissors. Use fancy two sided origami paper or even cardboard for something extra sturdy. Really, the combinations are endless.
I’m not quite good at knitting yet… but I do think making one of these for my knitting needles