The scientists developed ways to freeze embryos and eggs quickly using a method called vitrification. For this to work well, it needs a lot of a special liquid to protect the cells during freezing. They found that the usual liquid used in slow freezing isn't good enough for vitrification; it needs a better, less toxic liquid at higher concentrations. Some liquids work better and are less harmful than others. Now, they know that these freezing liquids need to get into the cells at the right speed to freeze them well. Different animals might need different liquids and temperatures for this to work. In their work, they figured out that the liquid used in vitrification needs to be chosen carefully to avoid harm to the cells.