When the Cat is spraying Lister with the can of beer that Lister cannot see, the spray is clearly coming out of the inside of the sleeve of Cat's jacket.
Why would Cat become invisible? He is not owned by any company.
Lister can't see his guitar but can hear it when he strums it. Yet he can't hear or see Kryton etc.
When Rimmer disappears, Cat reacts by turning and looking shocked, but Rimmer isn't invisible to Cat, and so Cat should have nothing to react to until Lister explains what has happened.