Sensory bottles! They used Voss water bottles. Not sure where to find them but any water bottle will work. use mineral oil for a way to slow down the materials in the bottle. I usually do 2/3 water to 1/3 oil. Can also do just rice and small objects for I-Spy bottles.
KID SAFE Two-Color Oil and Water Discovery Bottles @ Play Trains! These vibrant discovery bottles contain no lamp oil, using all edible ingredients to make them safe for young children to make themselves!