Det ligger smulor på bordet igen, så jag hämtar en trasa.

In this sentence, det is a kind of dummy subject. Swedish often uses det in sentences that introduce or describe the presence of something, especially when the real thing being talked about comes later:

• Det ligger smulor på bordet.
• literally something like There lie crumbs on the table.

This is similar to English there is / there are, even though Swedish uses det rather than a separate word meaning there.

So det here does not really mean it in the normal sense.

Ligga literally means to lie, but Swedish uses it much more often than English does for describing where things are.

So:

• Det ligger smulor på bordet = there are crumbs on the table / crumbs are lying on the table

Why ligger?

• because crumbs are understood as being physically resting on a surface
• Swedish often chooses a position verb like ligga, stå, or sitta where English would simply use be

Comparison:

• Boken ligger på bordet = the book is on the table
• Glaset står på bordet = the glass is on the table
• Tavlan sitter på väggen = the picture is on the wall

You could sometimes say det finns smulor på bordet, but that focuses more on existence: there are crumbs on the table.
Det ligger smulor på bordet sounds more concrete and visual: the crumbs are physically lying there.

Smulor is an indefinite plural noun, and in Swedish indefinite plural nouns normally have no article.

So:

• en smula = a crumb
• smulor = crumbs

This is normal Swedish grammar:

• Jag ser bilar. = I see cars.
• Det ligger böcker här. = There are books here.

You can add a word like några if you want to stress some:

• Det ligger några smulor på bordet.

But without några, the sentence is perfectly natural and often more neutral.

Bordet means the table. The definite form is built into the noun:

• ett bord = a table
• bordet = the table

Swedish usually uses the definite form when both speaker and listener are expected to know which table is meant, for example the table in the kitchen, dining room, or current room.

So på bordet means on the table, not just on a table.

Igen means again.

Here it shows that this has happened before:

• Det ligger smulor på bordet igen = there are crumbs on the table again

Its placement here is very natural. Swedish adverbs like igen often come near the end of the clause.

You may also hear slightly different placements in other sentences, but in this one på bordet igen sounds normal and idiomatic.

Because så here is being used as a conjunction meaning so, linking two clauses:

• Det ligger smulor på bordet igen, så jag hämtar en trasa.

After a coordinating conjunction like och, men, så, Swedish usually keeps normal main-clause word order:

• subject + verb
• jag hämtar

So this is like:

• ..., and I get a cloth
• ..., so I get a cloth

If så were instead used as an adverb at the beginning of a main clause, then inversion could happen:

• Det ligger smulor på bordet igen. Så hämtar jag en trasa.

But in your sentence, så is connecting the clauses, so så jag hämtar is the expected pattern.

Swedish often uses the present tense for something happening right now or in the immediate future, especially when it is a direct reaction or intention.

So jag hämtar en trasa can mean:

• I’m getting a cloth
• I’ll get a cloth

It does not have to mean a habitual action. In context, it clearly means the speaker is going to get one now.

You could also say things like:

• Jag ska hämta en trasa = I’m going to get a cloth

But jag hämtar en trasa sounds very natural when someone decides on the spot to do it.

Hämta means fetch, go and get, or bring back after getting. It suggests that the speaker needs to go get the cloth from somewhere.

• Jag hämtar en trasa = I’ll fetch a cloth

Ta just means take and is less specific:

• Jag tar en trasa = I’ll take a cloth

If the cloth is already nearby, tar may work. If the speaker needs to go get one, hämtar is better.

Because Swedish usually needs an article with a singular countable noun when it is indefinite.

• en trasa = a cloth / a rag

You normally cannot leave the article out in this kind of sentence.

Compare:

• Jag har en bok. = I have a book.
• Jag köper en stol. = I’m buying a chair.

So jag hämtar en trasa is the normal form.

Trasa usually means a cloth, rag, or cleaning cloth. In this sentence it suggests something used to wipe the table.

So it is not just any piece of fabric; it usually has a practical cleaning sense.

Depending on context, English might translate it as:

• cloth
• rag
• dishcloth
• cleaning cloth

In normal writing, the comma is common and helpful here because it separates two main clauses:

• Det ligger smulor på bordet igen
• så jag hämtar en trasa

Swedish comma usage can be a bit more flexible than English in some contexts, but this comma is natural and clear.

Not in standard Swedish as a normal statement.

A full declarative sentence needs a subject, and in this kind of presentational sentence Swedish uses det:

• Det ligger smulor på bordet igen.

Without det, it would sound incomplete unless you were using a very informal, fragment-like style.

It is both grammatical and idiomatic. Swedish often describes objects by their physical position more specifically than English does.

English often says:

• There are crumbs on the table

Swedish naturally says:

• Det ligger smulor på bordet

So even though lie sounds a bit too literal in English, ligger is exactly the kind of verb Swedish likes to use here.