The Elder Scrolls V: Skyrim – How to Manipulate Objects

Spells only create sound when they're actually cast (unless you have the illusion perk which negates the sound). Spells create light whenever they're selected, and even more when they're actually cast. (This is very similar to the self-illumination via pipboy in Fallout 3).

Given that you can't score sneak attacks with spells in the first place, keep your mage hands in your thief pockets when going in for a sneak stab.

They are in there, the new ones have made me laugh (especially the two-hander head banging)... But they are random. Getting them to show up is not a guaranteed thing. All I can suggest is keep playing.. I often work my combats to be 1 on 1 or 1 on 2 and such and I get the kill cam slo-mo quite often.