Learn Farsi: آنها اسب‌ها را در سیرک دواندند.

The base verb is دویدن (to run). To make it causative ("to make run"), we take its present stem, which is دو, and add the causative suffix ـاندن (-ândan). This gives us the new causative infinitive دواندن (to make run). Because this sentence is in the simple past tense ("they made run"), we drop the final ن to get the past stem دواند and add the "they" ending ـند, resulting in دواندند.

The present stem of "to run" is often pronounced "dow". Why does it sound like "dav" in دواندند (davândand)?

When the present stem دو stands alone or takes typical prefixes (like می‌دوم - I run), the و is usually pronounced as a diphthong like "ow". However, when you attach a suffix that starts with a vowel, like the causative ـاندن (-ândan), the letter و acts as the consonant "v" to bridge the sounds. So, it is pronounced "davândan" instead of "dowândan".

Why do we need the object marker را after اسب‌ها (horses) here?

The original verb دویدن (to run) is intransitive, meaning it doesn't take a direct object. But when you make a verb causative (دواندن - to make run), it becomes transitive—you are now doing the action to someone or something. Since "the horses" are now the specific direct object receiving the action, they require the marker را.

The lesson mentions the suffix . Could we use that here instead?