User blog comment:Lord Loss/Metal Gear Solid and MHP3 Crossover, Plus New Area (Arena?) Glimpsed/@comment-2158814-20100918143117/@comment-158109-20100919235941

Because in the original MGS games (and following ones), if you had one or more cardboard boxes in your inventory, you can use it to better hide yourself.

You'd move around in the box and peek out the hole.