Context: a couple is checking out the otters while visiting an aquarium.
Boy: 苗代【なえしろ】はカワウソが好きなの？
Girl: うん！動物で一番好き。食べる時とか時々ブサイクになるギャップがたまんないの。
What is the meaning of ギャップ in this sentence? Since she says "食べる時", I think maybe she is referring to the "gap" of an otter's slightly open mouth, but I am not sure. Here you can see the whole page. Thank you for your help!
It's from English "gap". She is referring to the large difference of an otter's face between when it's not eating and when it's eating. I guess she regards the former face as "handsome/cool" and the latter face as "relaxed and cute, although goofy in a sense". ブサイク is normally a negative word, but it's not always negative at least to some young girls...
Related:
不細工だが可愛いと感じられる顔立ちや表情を形容する表現。(snip)たとえば犬種のパグなどはブサカワであり、ブサカワであることがむしろ愛好されている種といえる。
I think the "ギャップ" is used as more of a colloquial usage than dictionary usage. I found the link : "かわうそファンが6年かけて発見！可愛いすぎる４つのポイント"
I borrow the different sentence how "ギャップ" is used from the site. The excerpt is
個人的にはアクリル板をカリカリする仕草がツボです。かわうそのやんちゃさが良く出ています…！ しかも、可愛いだけではないのがかわうそのすごいところ！水中をカッコよく泳いだり、時には野性味たっぷりに魚にかぶりついたり。さっきまで、あんなに可愛くしていたくせに…！でも、このギャップがかわうその魅力なんです。
I guess the author wants to describe in a same way. They always seem to behave cute and cool, but when it comes to eating they don't mind eating brutally. I think she wants to call the change of behaviors as a "ギャップ" rather than open of mouth.
Normally they are used in a positive way like "ギャップに萌える".
