You need to listen to the voice talking at normal speed, not the slow voice that separates every word. Because éléphant begins with a vowel it sounds more like zelephant when the leur is the plural "leurs". It is the only clue that you get...
Thank you Ruth. I tried to listen at normal speed, and usually, well most of the time, I am able to pick up that stuff, but in this case, after multiple tries, I could not pick up that z sound. That’s why I then tried the slow mode. When it comes to slow mode, it simply ignores the liaisons. On this occasion, both options failed to work for me, and that’s why I went looking for some other clue.
Unfortunately, it's the female voice, and "she" can't speak correctly and is unreliable. I don't hear a clear liason, so it's a guess as to whether it's plural elephants or not.
Duo needs to do something about the female voice. One moderator said they have no control over which voice "speaks", so I suggested getting rid of the female voice entirely. Not being sexist here - "she" just makes too many mistakes.
I asked the same question on french.stackexchange.com, and got the following response:
Are there any other clues the speaker had multiple elephants in mind? (This statement was part of my question. I wanted to know whether there are any other clues in the sentence itself — You can read the details here: https://french.stackexchange.com/questions/29992/when-listening-to-the-sentence-how-can-you-tell-that-they-are-talking-about-mor)
Certainly not. Proper liaison is the only clue.
The oral version of the following sentence without liaison ”Je parle de leurs téléphones” is 100% ambiguous.
Four strategies to resolve the ambiguity in cases like this:
Context. From what you know, do they jointly own an elephant or do they have a herd?
Agreement. Listen for an adjective that differs in the plural (éléphant royal / éléphants royaux) or a verb that does the same (éléphant qui boit / éléphants qui boivent).
Ask. « Parles-tu d'un seul éléphant ou de plusieurs ? »
Echo. When you talk about the same subject, choose an unambiguous wording (Donc, pour les éléphants ...) so they can straighten it out if you're wrong.
Though I love Duolingo, none of these options is possible with their isolated sentence system.
In slow mode, the speech lacks liaisons, which makes it impossible to tell whether they are talking about single elephant or multiple elephants. I rarely rely on the slow mode, but in this case I simply could not tell whether they were talking about an elephant or multiple elephants. The slow mode failed to address the problem.
The female voice makes clear that “leurs” is intended. The male voice is always difficult to understand.