Go! (usually while standing at the gate and shaking it)
woah! (like woah, horsey! except he usually says it in amazement of something)
uff uff uff (the sound a dog makes)
Ahhhhhhh! (loudly and high pitched to get attention or something he wants)
And many other words that definitely mean something. We just haven't figured them out yet. He'll make eye contact with us and tell us something. Or ask a question. He's quite sure he's talking. Some day soon it will be English!