I saw his look

There is no difference unless it is rethorical.
The '-ful' suffix gives the meaning something is full of a certain quality the morpheme suggests.

Thanks,

However, can "frightened" be used to replace "frightful" and "frightening"?

What does it mean in this case?

If I am sitting at my dinner table and a monster appears at my door, he looks frightening. The look on my own face is frightened.

If you yourself are feeling the emotion, you are frightened. If something about your appearance causes fright or alarm in others, you are frightening.

They are not at all the same.

Hi,

Let us make the sentence more easy to digest, shall we?

1. I saw a frightful look on his face.

2. I saw a frightening look on his face.

To me, the first sentence is saying that he had a frightful look (or frightened look) and that look is what I saw; whereas, the second sentence seems to be saying that he had on a frightening look (he looks to be scary) and

Both frightful and frightening describe the effect you have on others.

Only frightened means what that person is experiencing. Perhaps you mean fearful. If someone has a fearful look, that person is probably frightened.

Thanks very much,

In the end I have my own choice. It's frightened.

"I saw a frightened look on his face as he was wheeled into the operating room."

Thanks.

"frightened" is ok in your sentence. Yet "scared" & "panicky" could be other options, IMO..

Or ( )hitting bricks