"He loses his keys."
Translation:Han tappar nycklarna.
I checked wiktionary and it lists both "to lose" and "to drop (something by mistake)" [as well as to tap, like a keg, but I'm pretty sure that's unrelated ^_^].
Best guess is that the drop side of tappa's meaning is that you don't notice you've dropped it, therefore it's something you lose. The picture in my head for this sentence is a guy grabbing something out of his pocket and knocking his keys out without noticing.
What I don't know is, can tappar be a kind of general lost sort of verb for all things you misplace, or is it just for things you lose by way of dropping? I poked about on google translate and there are a lot of words for losing things in Swedish, so it might be more specific :|