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Frighten into doing
Negative Emotion
Using 'frighten into doing' suggests a strong negative emotion inducing action. It's more intense than just persuading or convincing. 
Lack of Consent
'Frighten into doing' implies that the action is against the person's will and is not a choice made freely. 
Power Dynamics
This phrase often suggests a power imbalance between the person frightening and the person being frightened. 