Over time, I've shared about a half-dozen video videos from the Pentatonix, an online a cappella singing troupe that has a unique sound and a loyal following.  As an interesting twist, this time they throw in an INSTRUMENT!  (I'm 90% sure it's a cello.)  There's even a drumtrack that appears late in the song as well!  Perhaps the Pentatonix are expanding their musical horizons a bit.  Check out this incredible version of a Great Big World's "Say Something"!