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Gravitrax PRO Splitter Expansion Set owls As they write on theSplit the directions of the marbles with the Splitter. See if the marbles have enough speed to roll across the trap door. If they roll too slow, the marbles will fall to awaiting tracks below and will go in different directions. Combine this accessory with any GraviTrax Starter Set. GraviTrax is a modular interactive track system where you can design and build your own marble runs. This STEM toy for boys and girls 8 and up, encourages experimenting