Usamos arnés y pies de gato.

Because usamos is the 1st person plural form of the verb usar (to use) in the present tense.

• yo uso = I use
• tú usas = you use
• él/ella usa = he/she uses
• nosotros/nosotras usamos = we use
• vosotros/vosotras usáis = you all use
• ellos/ellas usan = they use

In this sentence, usamos tells you the subject is we, even though nosotros is not written.

In Spanish, subject pronouns are often left out because the verb ending already shows who is doing the action.

So:

• Usamos arnés y pies de gato.
• Nosotros usamos arnés y pies de gato.

Both are correct, but the version without nosotros sounds more natural in many contexts.

Spanish does this a lot more than English.

Arnés means harness. It is singular here because it is being used in a general sense, not necessarily referring to one specific harness.

In Spanish, when talking about equipment, clothing, or things people typically use, it is very common to use the singular without an article:

• Llevo casco. = I’m wearing a helmet.
• Usa cinturón. = He/She wears a seatbelt.
• Usamos arnés. = We use a harness / harnesses.

So the sentence is not focusing on how many harnesses there are, but on the type of equipment used.

Pies de gato is the usual Spanish term in Spain for climbing shoes.

Literally, it means cat feet, which may sound strange to an English speaker, but it is a fixed expression. You should learn it as a vocabulary item, not translate it word for word in normal use.

So in a climbing context:

• pies de gato = climbing shoes

This is much more natural than trying to say something like zapatos de escalada in everyday climbing language in Spain.

Because climbing shoes come as a pair, and Spanish normally talks about them in the plural, just like:

• zapatos = shoes
• botas = boots
• calcetines = socks

So:

• pie = foot
• pies = feet

The expression is fixed as pies de gato, not pie de gato, when referring to climbing shoes in general.

Spanish often leaves out the article when talking about materials, clothing, tools, equipment, or things used in a general way.

So:

• Usamos arnés y pies de gato.

sounds natural when you mean we use harnesses and climbing shoes as equipment.

If you add articles, the meaning can become more specific:

• Usamos el arnés y los pies de gato.
  = We use the harness and the climbing shoes.
  This sounds like you are referring to specific items already known in the conversation.

• Usamos un arnés y unos pies de gato.
  = We use a harness and some/a pair of climbing shoes.
  This can sound more like talking about one set.

It is treated as masculine plural because the main noun is pies, which is the plural of pie, and pie is masculine:

• el pie
• los pies

So you would say:

• los pies de gato
• unos pies de gato
• estos pies de gato

The de gato part does not change the gender.

Yes, you might hear that, but it creates a slight difference in style.

• Usamos arnés y pies de gato.
  This sounds more general: we use that kind of equipment.

• Usamos un arnés y pies de gato.
  This highlights a harness a bit more as a countable item, while pies de gato still stays general.

Very often, the version without articles sounds smoother when listing gear in a general statement.

A simple pronunciation guide would be:

oo-SAH-mos ar-NESS ee pyes deh GAH-to

A few details:

• usamos → stress on sa
• arnés → stress on the last syllable because of the accent mark
• y is usually pronounced like ee
• pies sounds roughly like pyes
• gato has a clear hard g

In much of Spain, the s sound is crisp, and pronunciation is generally quite clear here.

The accent mark shows where the stress goes: ar-NÉS.

Without the accent, Spanish spelling rules would make you expect a different stress pattern. The written accent tells you that the final syllable is stressed.

So:

• arnés = stress on nés

Accent marks in Spanish are very important because they show correct pronunciation and sometimes distinguish between words.

Yes. Like many Spanish verb forms, usamos can mean either:

• we use (present)
• we used (preterite), depending on context

For example:

• Ahora usamos arnés. = Now we use a harness.
• Ayer usamos arnés. = Yesterday we used a harness.

In your sentence by itself, learners will usually interpret it as present tense unless the context suggests past time.

Yes, very likely. The combination of arnés and pies de gato strongly suggests rock climbing or indoor climbing.

That is why pies de gato makes sense here. Outside that context, the literal meaning cat feet would be confusing, but climbers immediately understand it as climbing shoes.

No, not in this sentence.

Spanish changes y to e before words that begin with an i sound:

• padre e hijo
• España e Italia

But here the next word is pies, which begins with a p sound, not an i sound, so it stays:

• arnés y pies de gato

That is the correct form.