Es manso y obediente cuando lo bañamos.

Because ser is usually used for traits seen as more inherent, typical, or defining, while estar is more often used for temporary states or conditions.

Here, manso and obediente describe the animal’s general temperament, so es sounds natural.

• Es manso = it is tame / gentle by nature
• Está tranquilo = it is calm right now

If you said está manso, it could sound more temporary or situational, depending on context, but es manso is the normal choice for a general characteristic.

Manso usually means tame, gentle, or docile, especially for animals.

It often suggests that the animal is not wild, aggressive, or difficult to handle. In many contexts, it fits animals better than people.

So in this sentence, manso y obediente gives the idea that the animal is easy to manage and behaves well.

Because obediente is an adjective that has the same form for masculine and feminine singular.

Many Spanish adjectives ending in -e do not change for gender:

• el perro es obediente
• la perra es obediente

They do change for number:

• el perro es obediente
• los perros son obedientes

So obediente works regardless of whether the animal is male or female.

Lo is a direct object pronoun meaning him or it.

It refers back to the animal being described. Spanish often uses object pronouns where English might repeat the noun less directly.

So:

• bañamos al perro = we bathe the dog
• lo bañamos = we bathe him / it

If the animal were clearly feminine, you might see la bañamos instead.

Because in Spanish, direct object pronouns usually go before a conjugated verb.

So:

• Lo bañamos
• La vemos
• Los cuidamos

This is one of the basic word-order rules for object pronouns in Spanish.

With infinitives, gerunds, or affirmative commands, pronouns can attach to the end instead:

• vamos a bañarlo
• estamos bañándolo
• báñalo

But with a normal conjugated form like bañamos, the pronoun goes before it: lo bañamos.

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is.

Bañamos tells you the subject is we.

So both are possible:

• cuando bañamos al perro
• cuando nosotros bañamos al perro

But nosotros is usually unnecessary unless you want emphasis or contrast.

By itself, bañamos can have two possible interpretations in Spanish:

• present: we bathe
• preterite: we bathed

In this sentence, cuando lo bañamos is normally understood as when we bathe him/it, because the whole sentence describes a usual behavior or repeated situation.

Context makes the present meaning clear here.

Because lo is already the direct object pronoun.

When you use the full noun for a person or specific animate being, Spanish often uses the personal a:

• bañamos al perro
• bañamos al niño

But when you replace that noun with a direct object pronoun, you do not keep the a:

• lo bañamos
• la bañamos

So lo bañamos is exactly what you would expect.

Grammatically, it could be about either, but it sounds much more natural for an animal, especially because of manso.

Manso is very commonly used for animals to mean tame or docile. With a person, it can be used, but it is less neutral and may sound literary, old-fashioned, or context-specific.

So most learners would naturally understand this as referring to a pet or another animal.

Spanish, like English, can link multiple adjectives after one verb using y.

So:

• Es manso y obediente
• Es grande y fuerte
• Es inteligente y amable

You do not need to repeat es before the second adjective unless you want special emphasis.

Yes. In this sentence, cuando is best understood as a general when/whenever.

It introduces a habitual situation:

• Es manso y obediente cuando lo bañamos
  = he/it is tame and obedient when/whenever we bathe him/it

Spanish often uses cuando this way without needing a separate word for whenever. Context tells you it is a repeated situation, not just one single event.