Later kom sy agter dat die hond onder die bed slaap.

The full verb is agterkom, which means to realize, to find out, or to discover.

In a main clause, Afrikaans often splits this kind of verb:

• Sy kom agter ... = She finds out ...

Here:

• kom is the finite verb
• agter is the separable particle

So Later kom sy agter ... is normal Afrikaans word order.

You will often see the full form agterkom in other structures, for example:

• om agter te kom = to find out

Because Afrikaans is a verb-second language in main clauses.

That means the finite verb normally comes in the second position of the clause. If you put Later first, the verb kom must come next, and the subject sy follows it:

• Later kom sy agter ...

If you started with the subject instead, you could say:

• Sy kom later agter ...

Both are correct, but fronting Later gives the time word a bit more emphasis.

Dat means that.

It introduces a subordinate clause:

• Later kom sy agter dat die hond onder die bed slaap
• Later she finds out that the dog is sleeping under the bed

In everyday English, that is often omitted, but in Afrikaans dat is very commonly used in this structure.

Because the clause after dat is a subordinate clause, and in Afrikaans subordinate clauses usually push the verb to the end.

So:

• main clause: Later kom sy agter ...
• subordinate clause: dat die hond onder die bed slaap

That final slaap is exactly what you should expect after dat.

Afrikaans often uses the simple present tense where English would use either:

• sleeps or
• is sleeping

So:

• die hond slaap can mean the dog sleeps or the dog is sleeping

If you want to stress that the action is in progress, Afrikaans can use other constructions, for example:

• Die hond is besig om te slaap = The dog is busy sleeping / is sleeping

But plain slaap is very normal.

Afrikaans verbs usually do not change form for different subjects in the present tense.

So you get:

• ek slaap = I sleep
• jy slaap = you sleep
• sy slaap = she sleeps
• die hond slaap = the dog sleeps

Unlike English, there is no special -s form for third-person singular.

Yes, here sy means she.

Afrikaans sy can also mean his in other contexts:

• sy hond = his dog

But in this sentence, sy comes where a subject pronoun goes:

• Later kom sy agter ...

So here it clearly means she.

Because die is the definite article the.

Afrikaans uses die for:

• singular nouns
• plural nouns
• all grammatical genders

So:

• die hond = the dog
• die bed = the bed

English speakers often expect different forms, but Afrikaans keeps this part simple.

Yes.

• onder = under
• die bed = the bed

So:

• onder die bed = under the bed

The word order is the same as in English: the preposition comes before the noun phrase.

Also, Afrikaans does not mark case on the article here, so you just keep die unchanged.

Yes, absolutely.

Both of these are correct:

• Later kom sy agter dat die hond onder die bed slaap
• Sy kom later agter dat die hond onder die bed slaap

The difference is mainly emphasis:

• Later ... puts focus on when
• Sy ... is a more neutral subject-first order

So the original sentence is not strange; it is just highlighting later.