SCP-055 is an object whose nature is forgotten immediately by anyone who sees or encounters it. Staff can never recall what it is, recording only negative clues such as "it is not spherical" or "it is dangerous," so the entire entry is filled solely with a list of what it is not.
The heart of the horror is an inversion of the record. Normally a record pins its subject down, but here the more it is observed the more information leaks away, leaving nothing in hand. The antimeme structure — unable to retain what was seen, accumulating only an empty space — turns the theme that observation and record cannot guarantee truth inside out.