Geckos dangling precariously from overhead lights or running up walls are a common sight in tropical countries. This is possible due to a weak attraction between the molecules known as the van der Waals force.
However, this force alone isn’t sufficient. To overcome this shortcoming, geckos have hundreds of minute and microscopic hair known as setae that cover their rounded toes. The setae synthesise conditions similar to a suction pump that enable geckos to adhere to apparent smooth walls and even upside down.
As the setae are bent downward and to the rear, geckos curl their toes upwards to disengage them. Hence, a gecko curls and uncurls its toes to synthesise a suction pressure that enables it to cling onto the walls.