In this task, you are given a paragraph, and your task is to construct a question from the given passage. Construct question in such a way that (i) it is well explained in the paragraph, (ii) the words may/may not be present in the paragraph, (iii) it should start with what/how/describe. Avoid creating a question that (i) is just relevant to one or two sentences, and (ii) not relevant to passage. 

Electrical signals in the brain travel through nerves to muscles. Two types of proteins exist in filaments in the muscles. The filaments move when the brain instructs them to. The motion of the filaments cause the muscle to shorten and contract. Opposing pairs of muscles exist in order to provide the necessary range of motion. 
How do muscles work?

A butterfly lays an egg. A larvae matures inside of the egg. The caterpillar hatches from the egg. The caterpillar eats and grows. The caterpillar spins a coccoon around itself and forms into a pupa. The butterfly forms inside of the coccoon. The mature butterfly emerges from the coccoon. The butterfly mates. The female butterfly lays eggs. 
Describe the lifecycle of a butterfly

The inner portion of the ring is formed during rapid spring growth. The tree's growth slows as the seasons change. The ring's outer growth is more dense. The growth of the tree pushes out the bark of the tree. The tree stops growing quickly in the winter. This seasonal "pause" in growth results in distinct rings in certain tree types. 

How do rings form inside the trunk of a tree?