At first glance they don't seem to imposing and only a bit on the bizarre side of things. This is BioShock after all. What is interesting her though is that these seem to be what will be taking over for those damned alarms from the first two titles. The big difference is that these things will roam and I think it is safe to assume that they can't be hacked. Well hacked in the traditional way while I am sure you can still "hack" them using melee or blunt weapons in the game to kill them.
As seems to be the case since the showing of the Motorized Patriot there isn't much else shown or talked about the Boys of Silence. No specifics on attacks or how they will interact in the game, well outside of calling in loads of back up if they hear you with their gaping mouths. That and the fact that they seem to only be featured in specific levels that will require stealth or an ass ton of bullets, I assume. Either way I can't wait to "hack" these things.
Here's the clip for your viewing pleasure.