A special effects call for “clouds” means there will always be science behind it somehow.
Sometimes “clouds” are needed as a special effect to move low across a set or a stage. This creates a dramatic effect for a dream sequence, a spooky scene, or someone flying. The special effects crew has a few tricks up their sleeves to pull it off, too. While it looks really cool, liquid nitrogen IS really cool at about -320℉ (-196℃). This effect takes training and uses equipment not usually laying around a home so leave it to the experts (but enjoy the video).