Throughout the book, the Professor is often seen watching the children through his window. But he never chases them away, and he also never approaches them when they're playing. So why watch? It seems as though the Professor has trapped himself behind this window, and that he is afraid to open it and let in normal life or other people. Pretty deep, huh?
However, when he sees April and Marshall being attacked by the murderer, the Professor knows that the time has come for him to do something:
"When I saw—when I realized what was happening, my first reaction was the natural one. I grabbed up a block of wood—but then, twenty-five years of self-imprisonment took control. I couldn't bring myself to break the glass and call." (23.27)
The Professor finally gets over his fear and breaks the glass. He calls for help—and in doing so, is finally able to break down his self-imposed walls and let other people into his life again. Not to mention save April and Marshall's life. Good thing he got over the stage fright.