“The initial water droplet expands as it shifts from liquid to vapor (top). At a critical volume, the expansion occurs explosively (middle), causing the bubble to over-expand relative to the pressure of the surrounding fluid. The higher pressure of the oil around it collapses the drop, which then re-expands, creating the cycle http://io9.com/heres-what-happens-when-you-throw-water-into-hot-oil-1729739429
“Drop of water in hot oil.”
Image courtesy of https://imgur.com/gallery/idnKfht.