I know in Snape's worst memory he casts a version of it to incapacitate James and Lupin would later remembers the effects of the spell.

In the Shrieking Shack when Snape shows up, he seems to imply that he could "do it".

Sirius sort of cowers and Lupin tried to talk him down, but is obviously fearful.

Do you think it's possible that Sirius could have been struck by the spell at some point and understood the repercussions of it?

We know Snape has a counter spell to reverse the damages of it. I feel it's possible Sirius could have found himself on the receiving end of it at some point or another.

Now we also know Snape is an exceptional duelist, and bullies typically grow to regret their actions when they realize that the tormented is now capable of tormenting.

Voldemort literally sent Snape on a spying mission. If his Death Eater status was known, then this wouldn’t have happened.

Karkaroff lists off Death Eaters and their crimes in his trial and only right at the end after a long thought, did he mention Snape without any mention of a crime.

The Death Eaters outnumbered the Order 10-1, there would be no reason why Snape, a Potions expert would be frequenting battlefields.

Also, this question is both book and movie related. I feel the movie captures this question pretty well, all things considered, but the book gave a much longer version of this with more information.

What are your thoughts? rar