Several characters within the Westworld control center are robots, not humans. Bernard Lowe, Theresa Cullen, and probably others. They were surprised to learn they were not human, or died without learning the truth about themselves.
These characters should learn very quickly they are not human. They would have different bodily functions than humans for food intake and defecation. Unless they were programmed to get tired, belch, sneeze, and cough like humans, they would have no need for those actions.
They would not get sick, but would see their coworkers take time off for the flu or a common cold. They would not age, but would see their coworkers slowly age over several years.
Memory works differently for humans than for robots. Human memory is vague, but robotic memory is so precise it is as though they relive the experience each time they remember a moment. They would be able to recall a memory from long ago exactly as it happened unless they told/programmed to "forget" it.
Humans should be able to remember key events from their childhoods and adolescence. Robots have neither a childhood nor an adolescence, so they should have no such memories unless several years of memories were implanted.
The point is they should have several clues which all point to the fact they are not like their human coworkers.
Shouldn't several characters have learned years ago they are robots?
I am only through the first season, so if this question is answered in a later episode, go ahead and mention that in an answer.