Horses and Tigers
In my opinion, that’s for good reason. It sounds absurd. It’s not some cool chengyu 成語 idiom with a neat story. It’s not bad ass in any way.
And, it turns out, it’s only just barely Chinese. It’s actually from Manchu lahū meaning unskilled, particularly in terms of hunting. Norman gives the following definition:
1. not adept, unskilled (especially at hunting and dealing with livestock) 2. scoundrel, hoodlum
The next entry in his dictionary is lahūta which means ‘a type of small, rather incompetent hawk’. I pray the two words are related.
Due to Manchu influence on Northern Chinese dialects, lahu was borrowed in and redupicated to lalahuhu which evolved into mamahuhu, horse horse tiger tiger.