Placenta dulcis bene olet.

Yes—this is a classic false friend for English speakers.

In Latin, placenta means a kind of cake or flat cake. The English anatomical word placenta is a later medical use of the same word, based on its flat, cake-like shape.

So in this sentence, placenta is an ordinary noun meaning cake, not the anatomical organ.

Placenta is nominative singular.

That tells you it is the subject of the sentence: the thing that is doing the action of olet.

It belongs to the first declension, so its basic form is:

• nominative singular: placenta
• genitive singular: placentae

In Latin, adjectives can come before or after the noun much more freely than in English.

So:

• placenta dulcis
• dulcis placenta

both can mean sweet cake.

What matters most is not position, but agreement.
Here dulcis matches placenta in:

• gender: feminine
• number: singular
• case: nominative

So dulcis is clearly describing placenta.

Dulcis is the nominative singular feminine form here, agreeing with placenta.

It comes from the adjective dulcis, dulce, meaning sweet.

This is a third-declension adjective, and one thing learners often notice is that:

• dulcis can be masculine nominative singular
• dulcis can also be feminine nominative singular
• dulce is neuter nominative singular

So in this sentence, dulcis is feminine because it describes placenta, which is feminine.

Because bene is an adverb, while bonus, bona, bonum are adjectives.

Here bene modifies the verb olet, not the noun placenta.

Compare:

• placenta dulcis = the sweet cake
  
  • dulcis describes the noun
• bene olet = smells well / smells good
  
  • bene describes the verb

English often uses good where Latin uses an adverb like bene.

Literally, it is something like smells well, but idiomatically it means smells good or has a pleasant smell.

The adverb bene means well, and olet means smells / gives off a smell.

So bene olet means that the smell is pleasant.

A useful contrast is:

• bene olet = it smells good
• male olet = it smells bad

Olet is:

• present tense
• active voice
• indicative mood
• third person singular

It comes from the verb oleo, olere, meaning to smell or to give off a smell.

It is third person singular because the subject, placenta, is singular.

So:

• placenta ... olet = the cake smells
• if the subject were plural, the verb would also be plural

Usually here it means to give off a smell.

That is an important distinction for English speakers, because English smell can mean two different things:

• I smell the cake = I detect the smell
• The cake smells good = the cake gives off a pleasant smell

In Placenta dulcis bene olet, the second meaning is intended:
the cake gives off a nice smell.

Because Latin has no articles.

Latin does not have separate words that directly correspond to English the or a/an.

So placenta dulcis could be understood as:

• a sweet cake
• the sweet cake
• sometimes just sweet cake

The exact choice in English depends on context, not on a Latin article.

The word order is perfectly natural Latin, but Latin word order is much freer than English word order.

Here we have:

• Placenta = subject
• dulcis = adjective describing the subject
• bene = adverb
• olet = verb

A few other arrangements could also work, for example:

• Dulcis placenta bene olet
• Placenta bene olet dulcis would be much less normal for this meaning, because dulcis would be awkwardly separated in a way that could confuse the structure

The sentence as given is straightforward and easy to understand. Also, putting the verb olet at the end is very common in Latin.

A common reconstructed Classical pronunciation would be approximately:

plah-KEN-tah DOOL-kis BEH-neh OH-let

A few details:

• c is always hard, like k
• ae is not present here, so placenta is pronounced with simple vowels
• e is like e in met, not like English ee
• bene has two clearly pronounced vowels: BEH-neh

So the whole sentence sounds something like:

plah-KEN-tah DOOL-kis BEH-neh OH-let