The postage meter indicia on the telephone bill says .4¢, a common current-day mistake--using a decimal point before the numerals followed by the cent sign resulting of four tenths of a cent rather than four cents. An actual postage meter would print either $0.04 or 0.04.
When Betty places a call, a modern dual-tone dial tone is heard rather than the "buzz" dial tone in use in 1960.
When Don and Harry are talking in Don's office late at night, Harry reveals that he was an amateur photographer in college and did a project of hand prints on glass. He then mentions how he was always fascinated with the cave paintings at Lascaux France, especially the "hand prints with paint blown all around". The hand prints he is referring are not at Lascaux but rather are at Pech Merle.