I'm guessing in this sentence, Duo is considered masculine, which is why مُمتِع is in the masculine form, rather than the feminine form? https://en.wiktionary.org/wiki/%D9%85%D9%85%D8%AA%D8%B9
Interesting. I've always considered Duo a male owl, probably because of the -o ending.
Hovering over ممتع gives two different meanings: interesting / fun. I wouldn't know how to opt more for one or the other. Duo here has chosen 'fun'. It might as well have been 'interesting'. ... Any help?