When Rogier finds a skeleton in the tunnel, the cowl of his tunic is on his right shoulder. Then the shot cuts to an angle showing him from behind and now the cowl is hanging on his back.
Although the bombardier claims he is the only person able to operate the Cupper Dog canon, most of the process is just like any canon at the time, which should be easy to remember for Meindert. The only really crucial point is the amount of gunpowder: 4 pounds. It seems strange that Meindert is not able to remember any of this by writing it down and seems to have forgotten all of it the next morning, when his writing has been changed to 14 pounds, which doesn't make him suspicious at all.