Sin que nadie lo note, mi amigo recoge las sillas y quita el polvo.

Because sin que is used when a new verb with its own subject follows.

In this sentence, after sin que, we get nadie lo note:

• nadie = the subject
• note = the verb

So the structure is:

• sin + infinitive when there is no new subject
  
  • Se fue sin decir nada
• sin que + subjunctive when there is a new subject
  
  • Se fue sin que nadie dijera nada

Here, my friend does one action, and nobody is the subject of the other clause, so sin que is needed.

Because sin que normally triggers the subjunctive.

So:

• sin que nadie lo note not
• sin que nadie lo nota

This is a standard rule in Spanish: expressions like sin que, para que, antes de que, and a menos que are usually followed by the subjunctive.

Here, note is the present subjunctive form of notar.

Lo is a direct object pronoun meaning it.

In this sentence, it refers to what your friend is doing, or more generally the action / the fact that he is doing all this.

So sin que nadie lo note means something like:

• without anyone noticing it
• without anyone noticing what he is doing

Spanish often uses lo this way to refer to a situation or action that is understood from context.

Because notar takes a direct object, not an indirect one.

• notar algo = to notice something

So:

• nadie lo note = nobody notices it

You would use le for an indirect object, but here the thing being noticed is the direct object.

Here recoger most likely means to pick up, to gather up, or to put away / tidy up the chairs.

Depending on context, recoger can mean several things:

• to pick up
• to collect
• to gather
• to tidy away

With las sillas, it probably suggests that your friend is moving them, stacking them, or putting them back in place rather than simply touching them.

Spanish uses definite articles much more often than English.

So where English might say:

• picks up chairs
• dusts

Spanish often says:

• recoge las sillas
• quita el polvo

The article does not always mean a very specific the in the English sense. It often just sounds natural in Spanish when talking about objects involved in an action.

Quitar el polvo is a common expression meaning to dust or to remove dust.

Literally:

• quitar = to remove / take away
• el polvo = the dust

So the phrase means:

• to dust the furniture or room
• to wipe dust away

It is more specific than limpiar, which means to clean in a general sense.

Because quitar el polvo focuses specifically on removing dust.

Compare:

• limpiar = to clean in general
• quitar el polvo = to dust / remove dust

So if the sentence wants to show a specific household task, quita el polvo is more precise.

In Spain, quitar el polvo and pasar el polvo are both common ways to talk about dusting.

Literally, nadie means nobody / no one.

In this sentence, sin que nadie lo note means:

• without anybody noticing it
• without anyone noticing it
• without no one noticing it would be wrong in English, but normal logic in Spanish allows nadie in this kind of structure

So in natural English, you would usually translate it as without anyone noticing.

It is placed first for emphasis and style.

Starting with Sin que nadie lo note highlights the idea that the action is done unnoticed. It sets the scene before telling us what the friend does.

Spanish word order is flexible, so you could also say:

• Mi amigo recoge las sillas y quita el polvo sin que nadie lo note

That would still be correct, but the original version gives more emphasis to the secretive or unnoticed way the actions happen.

They are in the present tense because the sentence is describing an action as a general statement, a habitual action, or a vivid present-time scene.

Spanish present tense can be used for:

• something happening now
• something that happens regularly
• a vivid narrative description

So mi amigo recoge las sillas y quita el polvo could mean:

• he is doing this now
• he usually does this
• the speaker is describing the scene vividly

The exact interpretation depends on context.

Yes, amigo is masculine, so it normally refers to a male friend.

If it were a female friend, it would be:

• mi amiga recoge las sillas y quita el polvo

Also, because Spanish often drops subject pronouns, the noun mi amigo makes the subject explicit here.

In this sentence, lo most naturally refers to the action or what is going on, not specifically him as a person.

So nadie lo note is better understood as:

• nobody notices it
• nobody notices what he is doing

If you wanted to say without anyone noticing him, Spanish could also use:

• sin que nadie se dé cuenta de él or other context-dependent wording.

So here the focus is more on the unnoticed activity than on the person alone.