Both of the dramas' main leads are math teachers and a lot of maths are shown in both of the dramas.

Both are kind of biography of the leads. In both of the drama, the story revolves around one main case. In case of big mouth, it revolves around seo jaeyeong's paper and in why her, it's an accident and SA case.
In both of the drama, antagonist boils your blood but still dies peacefully.

The title say that they should be fully different movies, but these two has similar plot and A Taxi Driver is more worthy to watch than this. The both movies show war between public and the police even though in Psychokinesis, they are not real police.

The story of the both dramas is same , but if you want to watch something quick then splash splash love is really good.

In both of the dramas the female lead first forced by their mother to play piano and at the end they also realise that they love playing too. Parents- children feud can be seen in both of the dramas.