Things are getting tense...
We know that there have been orcs wandering around Middle-earth for a while, having escaped the destruction of Utumno; they're why the Laiquendi headed to Beleriand, for instance. But I assume that until Morgoth's return to organise them they mostly avoided Thingol's kingdom; so while experienced and well-travelled warriors like Mablung might know what they are, more sheltered Sindar have never heard of them until now.
Also, please fill in my poll!
Part 209: To arms!
Next time: Part 210: Stratagems
Chibis by the now-dead website formerly known as tektek.org