Also, I see some of these clips on YouTube. Not sure if it is ok to take from there.

My thinking is that on all/most movies it says, copying any part is illegal.

Read up on Fair Use - it will make your head spin!

You might be fine, you might be in a gray zone, or you might be in position to get your balls sued to the wall.

Basically, no. Not without permission from the copyright owners.

If you write a 'scholarly document' that defines just what 'scary moments' are, uses such moments from classic movies to illustrate your point, gives full and proper citations for each 'quote' and maybe even rates the effectiveness of each moment, then that most certainly falls within 'fair use' because you are, in effect, quoting a small portion of the copyrighted work in order to reinforce your point.

Should you write a series of such documents (scariest, goriest, tenderest, meanest, etc.), your foundation of fair use will become more solid with each one written. Of course, authoring a serious document is more akin to work than fun, but there are those of us who think it's fun anyway, regardless of how much work is involved.

A couple 'scary' examples I immediately think of are when the detached head first 'jumps' into the scene in "Jaws", and when the hand comes down on the shoulder in "Phantasm" (though this one is definitely amplified when you sneak up behind someone and gently put your hand on her shoulder at the very same moment; you shouldn't ask how I know ).

If any and all copying violated copyright law, then everyone who ever quotes anyone else is guilty of copyright violation and must be sued, fined and/or jailed.