Every now and then (yesterday morning being the "then" in this case), Trevor begins to bark at something only he sees. it's confusing. And you have to find what he is seeing to tell him you see it and it is okay.
This is what caused barking yesterday morning at 7:30 (too early for Where's Waldo). We looked out the window in vain.
Nothing, right. We had to approach the window, zoom in, and then spot it.