Subject: pulse in carotid artery

I read frequenty to make sure when taking a pulse in the neck that you don't 
press both sides of the neck together due to it being a major artery.  What 
will happen if you do?  Will it cause permanent damage?  What if the artery is 
just narrowed but not completely blocked off?  Is there damage?  I haven't been 
able to find anything to answer this question. 

Re: pulse in carotid artery