Write a hypothesis about what causes the aliens change their shape

Hypothesis 1: The life form is incredibly sensitive and responsive to its environment and will change its form accordingly to accommodate the differences. This is achieved through incredibly adaptable and versatile organs as well as some processes that resemble capillary action and osmosis.

Hypothesis 2: The life form is composed from strands of pure energy (probably tachyon particles) actually held together by a field of gravity they generate themselves. These strands are constantly in motion.  Sometimes the gravity isn't evenly distributed due to the shape of the body, causing waves of particle to constantly fly off. The result is something that resembles a solar storm as well as a loss of body mass.

Hypothesis 3: Because it is a living thing! Cells need to be able to move and divide depending on changes in the surroundings.