speed of sound varies. and infants blinking

The speed of sound varies depending on altitude, temperature and the medium through which it travels. When a sound wave hits a molecule it will vibrate, thereby transferring the vibration to adjacent molecules, which is pass on continuously. Sound travels faster through steel as the molecules are close together unlike air which the molecules are far apart.

Normal babies rarely close their eyes, except of course when sleeping. infants blink on average less than twice a minute, a rate that steadily increases up to the age of 14 or 15. Adults, on average, blink about 10 to 15 times a minute.Blinking serves primarily to coat the eyes with tears and remove any dirt or debris from the surface of the cornea. So another theory is that infants, perhaps because their eyes are better protected by smaller openings or because they sleep so much, may require less eye lubrication.

(http://www.nytimes.com/2008/12/09/health/09real.html)