A one way mirror would probably work as well.
Additionally, it would literally work since the inside of the backpack is much darker than the outside.
Let me too my toe in, just a little bit. 5 minute adventure, nothing big.
Edit: oh it's that stuff. I'm not into it, all is good.
Can't tell if this is a genuine question, or if someone else enjoys asking people what vore is as much as I do