Questions & Answers about Infans canem placidum tangit.
Because infans is in the nominative singular, the case normally used for the subject.
In Infans canem placidum tangit, infans is the one doing the action, and tangit is a singular verb, so they fit together: the child touches.
Because canem is the accusative singular form of canis.
Latin uses the accusative case for the direct object, the person or thing directly affected by the verb. Since the dog is what the child is touching, Latin puts canis into the accusative: canem.
So:
- canis = a dog, the dog, as subject
- canem = a dog, the dog, as direct object