"You can't whistle because the air pressure in the suit is only 4.3 [pounds per square inch], and normal atmospheric pressure is 14.7 psi, so there are not enough air molecules blowing by your lips to make a sound," he said.[...]
Jeff Hoffman, a retired astronaut with three spacewalks (including a mission to repair the Hubble telescope) has traveled 21.5 million miles in space. He said the technicians who trained him on spacewalks had told him that he wouldn't be able to whistle, but he says he tried anyway.
"I couldn't get one note out," he said.
Link -via First Things | Photo: NASA