The scientists wanted to understand how pressure and stiffness change inside mouse embryos during development. They used a special method involving lasers and tiny magnets to measure these factors in different parts of the embryos. They discovered that as the embryos grow, both the inner pressure and stiffness increase in the trophoblast (outer layer) and the inner cell mass (core) of the blastocysts. This information helps us learn how mechanical forces play a role in shaping and developing embryos.