I am dumb in that I didn't make the connection between the stairs and the harpies. I think perhaps if I had, I might have been more interested in going up and seeing what sort of treasure they had. I also wasn't in full "murderhobo" mode because I didn't think about doubling back and tryi...
If all other investigations fail to yield any info, Thanis attempts to gently raise, lower, and twist the arms and hands of the statue. He also closely examines the eyes to see if they resemble buttons to be pushed.
Thanis looks at the statue's head, arms, and legs to see if it looks like anything used to be on them or in them. If he comes up empty there, he looks around the room to see if anything's been discarded that may be of use here.