The fallout itself may appear as dry , ash-like flakes , or as particles too small to be visible ; in the latter case , the particles are often deposited by rain . Large amounts of newer , more radioactive particles deposited on skin can cause beta burns , often presenting as discolored spots and lesions on the backs of exposed animals . The fallout from the Castle Bravo test had the appearance of white dust and was nicknamed '' Bikini snow '' ; the tiny white flakes resembled snowflakes , stuck to surfaces , and had a salty taste . 41.4 % of the fallout from the Operation Wigwam test consisted of irregular opaque particles , slightly over 25 % of particles with transparent and opaque areas , approximately 20 % of microscopic marine organisms , and 2 % of microscopic radioactive threads of unknown origin
Castle Bravo
Castle Bravo
Mushroom cloud