Armstrong acknowledged Aldrin's completion of the post landing checklist with "Engine arm is off", before responding to Duke with the words, "Houston, Tranquility Base here. The Eagle has landed." Armstrong's unrehearsed  change of call sign from "Eagle" to "Tranquility Base" emphasized to listeners that landing was complete and successful. Duke mispronounced his reply as he expressed the relief at Mission Control: "Roger, Twan— Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We're breathing again. Thanks a lot."