Mucus in the poop can be a symptom of Giradia (which is a parasite). Any type of stress can make a tiny trace of Giardia become full-blown. A simple stool sample can diagnosis this. If it what he has, your mom may want to treat her dog, too as it can be very contagious from animal to animal. All bedding, clothings, toys will also need to be disinfected.
Good luck and hope it's nothing major!!!
__________________  Sissy & Angel |