You can let it slide with a "oh?" or you can take it seriously.

A normal person might spend a lifetime at it and still not succeed but faced with a determined Ren it was not greatly different from a normal cylinder lock.

"Well, even so my score is far above yours isn't it?" "What did you say!? If I was to go all out you'd be as nothing to me!"

The shirt she apparently seriously thought suited me I turned down and decided to accept a light blue polo shirt.

You cannot be serious.

Do you really love me?

Do you really mean it?

Do you mean what you say?

I mean it!

Are you sure?

I mean what I'm saying.

She took my joke seriously.

He started to study in earnest.

He began working in earnest.

He took the photos in earnest.

He doesn't mean it; he's just acting.

He's not serious about her at all - he's just playing with her.

He said in earnest that he would quit the company.

His threat got me to start studying seriously.

It was obvious to all that he meant it.