Geckos are famous for sticking to things without using any wet gunk at all – a gecko’s foot is completely dry. So how do they run up walls and over ceilings, without using glue? It turns out the atoms of geckos feet actually combine with the atoms of whatever surface they’re walking on, but only for an instant. This attractive force between atoms is named after Johannes Diderik van der Waals, a physicist who began his career as a school teacher. Van der Waals forces aren’t strong – in fact, they’re incredibly weak, and that’s the gecko’s secret! Gecko feet are covered in millions of microscopic hairs, and each one of them sticks to a surface with Van der Waals forces, making a very strong combined seal of individually weak bonds. When a gecko needs to move, it just peels each weakly-held individual hair easily from the ceiling. A strong but reversible adhesive!