Existing technology continued to present difficulties: in particular, animating hair turned out to be a challenge. Senior software engineer Kelly Ward spent six years writing programs to make it move the way they wanted. As late as January 2010, the directors were still not sure if the Rapunzel character's length of hair was going to work. These problems were finally solved in March: An improved version of a hair simulation program named Dynamic Wires, originally developed for "Bolt", was eventually used. To make hair float believably in water, and to surmount other similar challenges, discrete differential geometry was used to produce the desired effects, freeing the animators from executing these specific tasks directly, which would have taken days instead of minutes.