Modular robots present many advantages that open opportunities for novel applications and greater variability in operational parameters. We present PetRo (which stands for Pet Robot) as a modular throwable, self-assembling and reconfigurable pet robot. Some of the design challenges and solutions selected are explained as well as the two main applications for which the robot architecture is being developed: namely as a companion pet and for search and rescue operations. Although both applications are being considered, this paper places emphasis on the first and the potential for human robot interactive communication is highlighted.