Imagery:
O'Brien provides rich imagery of the pond as the sun is coming up, as well as the hue of colors that Ann speaks of as she gathers flowers. Ann gets the inspiration to go out after having a dream about her mother, and how her mother used to pick them every spring. The thick description of Ann's path - the fields, the valley, the rabbits, and bass jumping out the pond - all invite the reader to think with great consideration of the sources of Ann's happiness. Picking flowers on a spring morning is not something that is generally seen in such a celebratory light. It provides a contrast to the dystopian world that Ann occupies and also serves as a beacon of light in an otherwise bleak world.
Simile:
Then he stopped, and instead ran back to the wagon....He reached inside and took out a glass thing--a sort of tube with a metal rod in it, like a big thermometer. pg. 22
For addtional information, check out GradeSaver study guide for this unit, particularly the section labeled, Literary Elements.