A painted line is the lines that they paint on streets and in parking lots that tell people where to park, or when they can pass. When dew falls at night or it rains because the lines are paint water collects on them. Bella was wearing flip flops that the tread has been worn out on so when she stepped on the line with her shoes having no tread and the combintion of a little water it created a slick surface which caused her to slip and fall. I have done this more times than I can count. Though usually I do not fall... but... I have been known to fall. I hope this clears this up. Thanks for reviewing!