The most difficult thing in Chinese kung fu is to have pliable bones. To become supple enough, one has to practice for a very long time.
12 seconds sound clip from the Shaolin Chastity Kung Fu movie soundboard.
You can hear this line at 00:38:47.524 in the DVD version of the movie.
Quote context
[...]
- I'm fine, come on. Let's continue.
- This will turn your muscles really hard.
- But this does mean that you can sustain more punishment without it causing you serious injury.
- Hey, come on, quit, no, no, no, you're hurting me, hey. Hey, hey, no, no, no, let me go. Come on!
[...]