They are also called dance fads or dance crazes. Later crazes include the late-1990s Furby wave and the mid-2000s RoboSapien. The music inspired dance crazes such as The Stomp, The Frug, and The Watusi. It had "foisted on us [America] feeble ideas, questionable taste, quackeries and crazes". Popular items developed a secondary market and sometimes became the subject of "collectable crazes". Unlike crazes these voids do not transfer stresses.. Crazes generally propagate perpendicular to the applied tension. One of the popular dance crazes of the era was "The Stomp". It teaches viewers moves from the latest K-pop dance crazes. Contemporary sources for dance crazes include music videos and movies. This has led to various crazes for stereopsis, usually prompted by new sorts of stereoscopes. These imperfections include porosity, solid inclusions, voids, crazes, etc. The five remaining crews put their own spins on popular dance crazes. Under tensile stress, crazes (microcracks) are formed, which spread to the rubber particles. Crazes can be seen because light reflects off the surfaces of the gaps.