Hi Danielle, great playlist. I've been learning a lot about functions this year. I just had a thought and decided it might be ok to post it here as a comment - either as something that's useful for you making future videos, or perhaps for anyone watching this video. So, when I was first trying to get my head around functions, as a real newbie, the thing you do at 12:18 would have been something that really confused me. Because 'old_x' has already been used in other functions, when you use it as the argument in the adjust_x function, I would have not understood that it actually doesn't matter, *within the function*, what you call that argument. I didn't yet get the difference between the global environment and the function's closed environment. So using old_x here might imply that you're passing the global environment variable old_x to the function* and if you think that, then it can seem confusing what the function is going to do. * I get that the whole point is that you _are_ going to pass old_x to the function! But if you don't yet understand the difference between the *argument name* within the function, and the *value* that then gets passed to the function, it can be confusing when these things are called the same. Hope that makes sense!