 He realises that no one ever referred to him as Rimmer in front of Cassandra and since she doesn't know everything she may believe someone else is Rimmer and have predicted that that other person will die first.He manages to ruin Knot's jacket and gives him his own with his name tag on it as a replacement.When Cassandra sees Knot die of a heart attack she of course believes him to be named Rimmer so her prediction comes true.