"The green owl is cute."
Translation:Le hibou vert est mignon.
le hibou, pas l'hibou?... on ne dit pas le homme mais l'homme. is there a rule about this?
This is an example of an "aspirated h," h aspiré. Certain words in French beginning in h do not form a liaison between the last vowel in the proceeding word and the first vowel sound in the next word. The h is still silent, but it acts like a consonant and it sounds like there is a brief pause between the two words rather than the smooth liaison. Le hibou sounds like "luh eboo." Unfortunately these words just have to be memorized. Dictionaries will have an asterisk next to an h aspiré.
Here are some more examples: le hockey, la Hollande, le héron, le héros.
And a useful link: https://www.lawlessfrench.com/pronunciation/h-aspire/
Is le haricot in that category also? (In standard French; not in Cajun).
Yes, it's le haricot. If you look in a French dictionary, there will be an asterisk * next to words beginning in h that are aspirated.
This word 'cute' is not commonly used in English English. I think we might say 'sweet' - is here an alternative that wouldn't make me feel sick?
Since Larousse advises that "mignon" may be cute or sweet, Duo will allow "sweet" here.