Weird!

So the field behind our house has always had cows come and go. I think it is their stopping point to the slaughter house (sad, I know!). They are only there for a few weeks at a time through out the spring to fall. We had cows back there up until Wednesday of this week.

Yesterday our room got pretty hot so I opened our two windows ( one in the front, one in the back). We get a really good wind flow through our room when we do that. Last night they were still open while we laid in bed. We both heard a cow moo in the back and I thought "weird!" I told Matt that there was no cows back there anymore. He thought maybe they got a new herd last night. Well, maybe they did. We closed the window and went to bed.
This morning I got up before the sun and started my day. When the sun came up I let the dog out and noticed no cows. I went up to our master bathroom and looked out the window (to see the whole field). NO COWS! What did we hear last night?
I'm a little weirded out today!