They missed each other very much.
Meaning: This means that the cat and mouse felt sad and longed for each other's company.
Choice of Words: Missed means to feel sad or long for someone or something that is absent. Very means to a great extent or degree. Much means a large quantity or amount. When you put them together, "missed each other very much" means that the cat and mouse felt a strong sense of longing and sadness for each other.
Alternative Expressions
Related Expressions