Nac ydyn, dyn ni eisiau cath!
If course, in some (non-Welsh-speaking) parts of the world, this could also be translated as "Do we want some dog?" - in the same sense as "Do we want some egg fried rice?". Not that I am suggesting this translation should be added, mind you.
What is the difference in saying "Dyn ni eisiau ci?" To " Ydyn ni eisiau ci?" Or is this just a North / South thing?