Some synonyms for the phrase "scared stiff" include petrified, frozen with fear, paralyzed with terror, terrified, horrified, and panic-stricken. Each of these phrases conveys a similar sense of extreme fear or distress, but with slightly different nuances. "Petrified" suggests a fear that has immobilized someone, while "frozen with fear" implies an inability to move due to intense fright. "Paralyzed with terror" similarly suggests complete inability to take action due to fear. "Terrified" and "horrified" both convey a sense of overwhelming fear, while "panic-stricken" implies a fear that has caused someone to lose control. All of these synonyms illustrate the range and intensity of emotions associated with feeling scared stiff.