Patrolman Zwart chases down Hielke, Sietse and the Nozem from his police station and leaves the door open. But when they all run up the stairs and the Nozem stays behind, the door is closed.
Kees has whip cream on his ice cone while sailing. But in the next shot, it's all gone.
The reflection of the camera and the light can be seen in the sunglasses of the Nozem before attacking Kees.
Kees pulls the tin can telephone at home and this results in the tin can in the bedroom of Hielke and Sietse, which lies several kilometers further, tingling like a cowbell. But it's impossible for a tin can telephone to work over such a long distance or making sound.
When Hielke and Sietse spray the Nozem, the water is clearly not coming out of the fire hose.