Hydro does it when I'm telling him what to do or just messing with him he lets out a sassy wooo wooo wooo. Sometimes when he stretches he'll let out a whispering arrr wooooooo

Ginger will do it when we're watching tv and she wants to go outside, she'll stand at the door and if we ignore her she walk over to us, look us straight in the eyes with this frustrated look on her face and gives us a wooo, sometimes she'll throw in an errr to get her point across.