Who'd a thunk doing a water change would have brought the aggression out amongst my Chaetobranchus flavescens. Only lasted a few minutes, but was still cool to watch.They have HUGE mouths when flared. Unfortunately they were at the back of the tank, so I couldn't really get them. They only show those black verticle bars below the lateral line when they are grumpy!! Possibly horny? 
Added a shot of the acute...




Added a shot of the acute...



