Hey, I recently managed to play with some small magnet balls and created a simple riddle:

https://www.dropbox.com/s/raleq3lsuhjr4pz/Riddle.mp4?dl=0

Question is: how many balls are there?

I didn't do anything sly, interior is filled as tight as it can be. Of course it is rather simple, but I find it entertaining. Please use 'hide' tags for answers.

UPD: Congratulations to lmn0x4F on being first one to give correct answer :)! If you want to read my explanation and additional comment then look at my answer to rng_58's comment.