Yep the black lines are in the sand. The first one is just before the text line "it's hot...", the second one between the the word "obstacles" and the rock on the ground, the third one after the first platform, the fourth one after the text "some things in the desert.." between the two last cactus. The fifth is align with the end of the mini "moutain" of sand with a rock on it. The last one is before the three cactus section, but not like close, a little bit before. The last one is under the word "whew".
I did a screenshot for one of the line:
And that's it, everything else looks fine to me.