Penumbra: Black Plague Trivia
Early in the game, Philip discovers a slide projector with slide containing a timeline of the events happened in the mine. If you "use" it, Philip will write the timeline on his notebook except for one event:
"24th December 1970: Mine worker Tom Redwood goes missing"
Tom "Red" Redwood is the only human that we meet in the previous game, 30 years after he disappeared. This may be seen as an emotional attachment of Philip to his late friend.