"The robots ran."
-pu' is only used for the plural of beings capable of language and klingons generally do not consider robots to be "beings" even when they are capable of language.
A fairly good explanation is given in the Tips & Notes. If you have not been reading the Tips & Notes, I would like to ask that you review those so we don’t have to continuously repeat the information that we have explained there.
If you are doing the course on iOS or Android, you may not be able to currently access the Tips & Notes through the app. To access the Tips & Notes, you will probably have to access the course using a web browser at https://www.duolingo.com/. You can still do it on your mobile device, but you will have to use the web browser instead of the app (or you can do it from a computer, which will be a little easier to read). When you click on a Skill, it will expand to reveal a Start button and a light bulb.
If you click on the light bulb it will reveal the Tips & Notes and give you a detailed explanation of the grammar that is introduced in that Skill. If you have questions after reading the Tips & Notes for the previous and current Skills, then please return to the forum to ask your question, explaining what you didn’t understand or what seems contradictory to you.
Oh, I am so sorry I took up your time! I tried looking in the Tips & Notes (on a computer) first but didn't find it. Apparently because I hadn't reached the "Pronouns" unit yet and didn't think of looking there. I'm in the "Sent. 1" unit right now. I only looked in the units that I had already done.
Thank you again for all your hard work, and I will try looking in units past where I am next time. Qapla'!
No need to apologize. We're here to help, but since Duolingo has hidden the Tips & Notes, I like to make sure everyone knows about them.
Here is a quote from the Tips & Notes of the Simple Sentences (or Sent. 1) Skill that this sentence appears in:
"Beings capable of language take -pu' (tlhIngan "a Klingon", tlhInganpu' "Klingons").
"Body parts take -Du' (and will be introduced later).
Everything else takes -mey (nagh "a rock", naghmey "rocks").
"Note that Klingons do not generally consider robots (no matter how smart or independent) to qualify as "beings capable of language". Thus robots usually (and in this course, always) use the plural suffix -mey: one qoq, several qoqmey."