Corrected entry: When in the boat tunnel, we see a brief picture of 'Slugworth' being shown in the background. Both Charlie and Grandpa Joe react to it, even though there's no reason for Grandpa Joe to. He couldn't possibly think it was Slugworth, given how it was actually just an actor, Mr. Wilkinson, whom he has never even seen before.
MasterOfAll
17th May 2014
Willy Wonka & the Chocolate Factory (1971)
Correction: Correct. Slugworth gave Charlie a thumbs up before entering the gates. Charlie told his grandpa that was him to which grandpa looked at Slugworth. Therefore he would recognize him on the tunnel wall.
Correction: While waiting with the other winners to enter the factory, Charlie points out Sligworth to Grandpa Joe. They both recognize his picture in the tunnel and react the same, as they both know what he looks like and what his intentions are.
Correction: Grandpa Joe does not react to the photo of Slugworth, but to Charlie's calling and grabbing him.
MasterOfAll