the active glue traps use rapid plant movements to trap their prey. rapid plant movement can result from actual growth, or from rapid changes in cell turgor, which allow cells to expand or contract by quickly altering their water content. slow-moving flypapers like "pinguicula" exploit growth, while the venus flytrap uses such rapid turgor changes which make glue unnecessary. the stalked glands that once made glue became teeth and trigger hairs in species with active snap traps —an example of natural selection hijacking preexisting structures for new functions.