La infano ekridis, kiam mia avo rakontis amuzan ŝercon.

Ekridis is built from ridi = to laugh plus the prefix ek-.

The prefix ek- often means to begin suddenly or to start doing something. So:

• ridis = laughed / was laughing
• ekridis = burst out laughing / began to laugh

In this sentence, ekridis shows the moment the child started laughing, probably in reaction to the joke.

Ek- is a very common prefix. It usually gives the idea of a sudden beginning of an action.

Examples:

• ekkuri = start running
• ekparoli = start speaking
• eksidi = sit down suddenly / begin to sit

So ekridis is a very natural way to express started laughing or burst out laughing.

Rakontis is past tense.

Esperanto verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command / jussive
• -i = infinitive

So:

• rakontas = tells / is telling
• rakontis = told

Since the whole sentence describes something that already happened, rakontis is the correct form.

The -n marks the direct object.

In Esperanto, the thing directly affected by the verb usually takes -n. Here, the grandfather told a joke, so ŝerco is the thing being told:

• ŝerco = a joke
• ŝercon = a joke, as the direct object

So in mia avo rakontis amuzan ŝercon, the direct object is amuzan ŝercon.

Adjectives in Esperanto must agree with the noun they describe.

That means they match in:

• number: singular or plural
• case: whether the noun has -n

Here:

• ŝerco is singular
• ŝercon is accusative, so it has -n

Therefore the adjective must match:

• amuza ŝerco = an amusing joke
• amuzan ŝercon = an amusing joke, as direct object

This agreement is one of the most important patterns in Esperanto.

Kiam means when.

It introduces a time clause:

• La infano ekridis = the child burst out laughing
• kiam mia avo rakontis amuzan ŝercon = when my grandfather told an amusing joke

So kiam connects the two actions by time.

It can also be used in questions:

• Kiam vi venos? = When will you come?

The comma separates the main clause from the subordinate clause.

Main clause:

• La infano ekridis

Subordinate clause:

• kiam mia avo rakontis amuzan ŝercon

Using a comma here is normal and helps readability. Esperanto punctuation is generally fairly straightforward, and commas are commonly used before subordinate clauses like this.

La is the definite article, meaning the.

• la infano = the child

But possessives like mia, via, lia, and so on usually make la unnecessary:

• mia avo = my grandfather

In Esperanto, you normally do not say la mia avo in ordinary usage. The possessive already makes the noun definite enough.

Avo means grandfather.

Related family words:

• patro = father
• patrino = mother
• avo = grandfather
• avino = grandmother

So mia avo means my grandfather.

Esperanto word order is more flexible than English because endings show grammatical roles clearly.

This sentence uses a very natural order:

• La infano ekridis, kiam mia avo rakontis amuzan ŝercon.

Because ŝercon has -n, you know it is the object even if the order changes.

Still, some orders sound more natural than others. The given version is clear and idiomatic. Esperanto often uses flexible word order for emphasis, but beginners should usually stick to the most straightforward pattern:

• subject + verb + object

Yes. You could say:

• Kiam mia avo rakontis amuzan ŝercon, la infano ekridis.

This means the same thing. The difference is mostly emphasis and style.

Putting the kiam clause first can make the timing/background come first, while the original sentence starts with the main event: the child burst out laughing.

The letter ŝ is pronounced like English sh.

So ŝerco starts roughly like:

• SHER-tso

A rough pronunciation guide for the whole word:

• ŝerco ≈ SHER-tso
• ŝercon ≈ SHER-tson

Also, c in Esperanto sounds like ts, not like English k or s.

Infano means child and does not specify gender.

If you wanted to specify gender, you might use:

• knabo = boy
• knabino = girl

So la infano is a neutral way to say the child. Esperanto often allows you to be as specific or as general as you want.

Yes, it can.

The clause with kiam tells you the time relationship, but it does not force an extremely precise interpretation. The sentence can naturally mean that the child burst out laughing at the time the grandfather told the amusing joke, perhaps during the telling or in response to it.

If a speaker wanted to be more exact, they could add more context. But as written, the sentence is perfectly normal and natural.