Without any sort of cover on what he is doing, Hansel lets go of the stones from his pockets. Because he didn't care to hide his actions, the woman quickly noticed what he was doing.
"Hansel, don't go playing with rocks, you could have hurt yourself badly with these," the woman says as she makes Hansel remove the stones from his pockets. Hansel had nothing to make a trail with for the rest of the trip. The kids were unable to find their way home during the evening and eventually starved in the woods.
Should have at least coughed or pretended to vomit then drop a stone.