Belgian animator Stefan Vermeulen and I animated the characters in tvpaint, with help of live-action material that I shot with a couple of young actors.
The animation of the heads was not based on live-action but on animation that we did with clayheads first.
I then animated all facial expressions and painted the shadows frame by frame on top of the drawings that were colored flat by Marc Schopman.
We had to do 25.000 drawings this way and it took many years to finish it.
Luckily I had 9 interns over that period of time that helped us tremendously, Aimee de Jongh, Jan_Jaap Schraverus, Igor Duspara, Marlyn Spaaij, Jasper Kuipers, Jan Mumford, Isabel Sluitman, Anne Scholten and Joyce Stenneke.
Here you can see the 4 stages of a shot.