Continuity mistake: At the beginning of the movie, the Golden Tickets are placed over the upside-down chocolate bars, meaning that the tickets are actually on the bottom, but later when the children find the tickets, they are now on top of the bars.
Visible crew/equipment: When Charlie is shining Willy's shoes near the end, you can see the reflection of a crewman in Willy's glasses when he glances to his right. (01:38:25)
Continuity mistake: In the scene where Mike Teavee has smashed up the red pumpkin-looking thing, he smashes it cleanly into two or three quite big pieces. When his father says "Mike, please" the pieces behind him are much smaller and all over. (00:41:35)
Factual error: Dusseldorf does not, nor has it ever, looked like the quaint place shown in the film. The caption does get quite a laugh from German audiences, though. The place shown is the town of Gengenbach.
Answer: Wonka is simply uncomfortable around people. Gum chewing is simply an annoyance he never had to put up with as a recluse.
JC Fernandez