Thank you for your comment. Yes, it changes every 10 seconds, we thought about making it more random but it made the game extremely difficult and unfair.
We didn't had time to add sound because there were bugs to fix and the rock was implemented quickly because we needed more enemies and it isn't very well polished. The idea was that you have to avoid touching it no matter what, one with spikes would have been much better, now I see that it can lead to confusion.