You don't get to see your sister cry.
Why don't you conjugate the verb cry (...your sister cries)?
Is it because is it the second verb (if that's the case, what is that rule called?) or is there another reason? Does it have something to do with the sister being subject form? I know this is quite a dumb question but I couldn't find anything on Google. I know that it should be "cry" and not "cries" (I can hear that that's correct) but I can't motivate why.