After Penny coerces Vijay not to tell his dad about the robot, by holding hostage the envelope Vijay dropped on the trail, Penny is shown holding the white envelope behind her back as Judy and Will walk past her. Once they pass, she no longer has the envelope in her hand. Then in the following shot, as they head up the trail, she has the envelope in her hand again.
The hand images on the cave at Lascaux, France were not direct prints. They were created by holding a hand to the rock face like a frisket and then blowing the pigment to create a negative.