I suspect the problem is that matplotlib needs constant-length arrays to plot two on the same plot. For each 'tick' of the animate function it will need to know what value to write for that instant.

Advanced Matplotlib Concepts In this section we cover some more advanced topics which you won't usually use as often.

xkcd Plot Styles To generate plots that look hand drawn, in the style of the xkcd comic, we can use the plt.xkcd() styling option. To make the style only temporary we construct the plot under a with ...