i think the rats are just speaking in katakana sometimes which would be just translated phonetically by a translation tool. for example, "ウシロカラ" would be just turned into romaji as "ushirokara." but if you were to convert it to hiragana/kanji, "後ろから" would become "from behind." i've seen other mangas use katakana to show the speaker doesnt know the word they're saying, or how to speak the language very well, so it would make sense to me in this situation.