December 29, 1950: What were they doing?

I like the look on Snoopy's face here, resenting Charlie Brown's intrusion on his and Patty's private time.  But what were they doing?  Was Patty reading to Snoopy?  The current-day, South Park-informed joke to make here, of course, is to suggest some naughty activity they were engaged in.


I will resist these implications with every fiber of my being.