When the player and Cube are in complete darkness, the Cube can occasionally "stab" its owner, inflicting 3 damage. The stab can kill the owner if at low HP, with the unique death message "[Player name] was stabbed."
When the Cube falls into 熔岩, it emits the 拜月教邪教徒's death sound. When submerged in lava for long enough, there's a chance it may make the 月亮领主's death sound. The Companion Cube will also occasionally emit the flatulence sound normally produced by the 整蛊坐垫 and the items crafted from it (e.g. 罐中臭屁).
Like other pets, the Cube can activate 青绿压力垫板s.
it is one of two pets that can make noises, the other being the 宠物天虫.
- It is the most expensive single item in the entire game.
- When sitting in a thin amount of lava (like when the cube is mostly exposed to air, except for a small portion) and the player is standing still, the cube (when sitting in the lava) will bounce, disappear, then reappear (instantly) where the player is standing.
- The 拜月教邪教徒 sound will only play a maximum of once per minute, regardless of how many times the cube touches lava.
- The Companion Cube will move (and bounce repeatedly) through solid blocks to stay close to the player, if the player is more than 6 tiles away.
- The Companion Cube, if in complete darkness, does not need to touch you to stab you.
- The Companion Cube is a direct reference to the Aperture Science Weighted Companion Cube, from Valve's Portal game series, as is the fact that the Companion Cube can activate 青绿压力垫板s. The Companion Cube reacting to lava is a reference to how the Companion Cube is disposed of in Portal, by being dropped into an incinerator. The Companion Cube stabbing the player is a reference to a line spoken by GLaDOS in Portal, in which she states "The Enrichment Center reminds you that the Weighted Companion Cube will never threaten to stab you and, in fact, cannot speak." This line is also directly quoted in the Buff tooltip.