Originally Posted by Elli

The Case of the Locked Room

"I think I've been taken for ten thousand dollars, but I can't figure out how it was done," said Archer Skeat, the blind violinist, to Dr. Haledjian, as the two friends sat in the musician's library.

"Last night Marty Scopes dropped by," continued Skeat. "Marty had a ginger ale - and we got to chatting about the locked room mysteries till I made this crazy ten-thousand-dollar bet.

"Marty then went to the bar over there, filled a glass with six cubes of ice and gave it to me. He took a bottle of ginger ale and left the room.

"I locked the door and the windows from the inside, felt to make sure that Marty's glass held only ice, and put it into the wall safe behind you. Then I turned off the lights and sat down to wait.

"The bet was that within an hour Marty could enter the dark, locked room, open the locked safe, take out the glass, remove the ice, pour in half a glass of ginger ale, lock the safe, and leave the room, locking it behind him - all without my hearing him!

"When the alarm rang after an hour, I had heard nothing. Confidently, I unlocked the door. I kept Marty whistling in the hall when I crossed the room to the opposite wall and opened the safe. The glass was inside. By heavens, it was half filled with ginger ale and only ginger ale. I tasted it! How he do it?"

"Undoubtedly by means of an insulated bag," replied Haledjian after a moment's thought. "There is nothing wrong with your hearing. But no man could have heard-"

Heard what?

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Sorry, this is an extremely easy one.