What is the meaning of idiom 'Foar in the mouth'?

Q. What is the meaning of idiom 'Foar in the mouth'?

1. Frightened 
2. Be complacent 
3. To revive a quarrel which was almost forgotten 
4. To be furious

Answer: To be furious

Foam at the mouth: Be in a state of uncontrolled anger

Ex: She was almost foaming at the mouth when she heard about the cost of the car repairs. Walter was foaming at the mouth with rage.