Because there is a direct object.
Klingon verbal prefixes encode not only subject but also object (or lack of one) -- bI- is for "subject = you [one person]; no object" while Da- is for "subject = you [one person]; object = him/her/it/them".
The verb prefix Da- is introduced in the tips and notes for the very first unit: https://www.duolingo.com/skill/kl/Useful-phrases/tips-and-notes
Please make sure that you always read the tips and notes before starting a new unit.
You are hopefully using the web site https://www.duolingo.com/ to learn Klingon, as the tips and notes are not accessible in the mobile apps to must users.
On the website, click on a unit name and then on the lightbulb in the little window that will open:
If there is something in the tips and notes that you find confusing, contradictory, or missing, we're always open for suggestions for improvement -- we rely on people to read the tips and notes so that we only have to answer questions once, not hundreds of times scattered across dozens of sentence discussions, so we want the tips and notes to be as useful and understandable as they can.
There's a "pronunciation unclear" note on this from a learner. Firstly, thank you for indicating what you felt was wrong with the audio. So often people click that there's a problem with the audio and I'm left wondering what they didn't like. I ask myself if there's a crackle that my speaker doesn't amplify but yours do? Is there a breathing or other extraneous sound that I don't hear because my brain just filters for Klingon language and ignores the non-language? That's what brains do! They've learned to hear only the sounds and sound distinctions that make sense in the language you're expecting.
In this case one can actually hear every sound in both words. But because some of the sounds do not exist in English, your brain throws them away.
q is far back in the mouth, behind the position of English k, so your brain thinks the sound is mumbled or incomplete.
The S is retroflex, meaning the tip of the tongue is back rather than forward, so that if you're expecting an s it sounds mushy and indistinct. Same with the D.
The H sound isn't in English, but sometimes English speakers make that sound when they are breathing, so your brain filters it out.
The final o might sound sort of truncated, like I didn't finish saying it, or cut the mic too early. That's because it's followed by ', the letter qaghwI', the interrupter. That's exactly what it's supposed to sound like.
Keep listening, and after a while your brain will realize that the odd sounds are valid language pieces and will start to hear them properly. Eventually you'll have the experience of hearing someone speak a language you know that's not Klingon, but you'll be listening in Klingon, and hearing only the Klingon sounds, so not understand what they're saying until your brain switches.