The way she tells me what she wants and knows what I"m saying. If she's staring at me and barking at me and I ask her What? she runs over and tags what she wants with her nose or she'll run over and stare at it. When I say "I have to go get your food" she races for the basement door. Tell her it's time for bed, she races for the bedroom.
She is by far the smartest dog I've ever had. I think she understands more than she lets on.