馬の口

Idiom:

• Straight from the horse's mouth

= I heard it directly from the person in the story



Situation:

• A person tells you a story about himself/herself
• You tell another person the same story
• The other person thinks it is a rumour or a lie
• You say "I heard it straight from the horse's mouth."

Example:

Kazuhiko: "Natsumi had a date with the boss!"
Nanako: "No way; I don't believe that. Who told you?"
Kazuhiko: "It's true; I heard it straight from the horse's mouth." (Natsumi herself told Kazuhiko.)