Answer to Question 1
Answer: Sometimes portions of cumulonimbus clouds hang downward in sac-like shapes called mammatus. These features occur where downdrafts force water droplets below the cloud base or sloping edge of the cloud, usually near the anvil. Because of the high liquid water content of these clouds, the droplets contained in the downward-moving air require substantial descent (and resultant adiabatic warming) before they fully evaporate.
Answer to Question 2
Answer: cumulonimbus