What is ironic about the following lines spoken by Claudius your words fly up thoughts remain below Words without never to heaven go?

Claudius's lines, "your words fly up, thoughts remain below/Words without thoughts never to heaven go," are ironic because he himself is using empty words without genuine thoughts to further his deceitful motives. He accuses Hamlet of speaking without thinking, yet he is engaging in the same behavior by attempting to deceive others with his false assurances. In using these lines, Claudius unwittingly reveals his own duplicitous nature.