I would say the rubber duck part is the most challenging. My friends who tried the game were also stuck there and needed multiple tries to pass. Since I played the game a thousand times I intuitively pass it without any issues but upon the feedback I did not want to modify it because then I felt like the game/level would be too easy :D
The duck just puts a force on you upwards, thus; I think for the part you were stuck you need to land on the right side of the duck.
The scream is a famous scream called the "Wilhelm Scream" . It is used in many movies as an easter egg :D glad you liked it.
Thank you very much for playing. I get very excited for every comment I get!