Why were sentinels built with emotions?

[Mdriver1981]

Often during battles, the sentinels show emotions on their robotic faces. Emotion like bewilderment, fear, anger, etc. Why did the people that built them program them to have and show emotions? This time and money consuming adage makes no sense and allows them to show weakness. Also, why do sentinels communicate with each other audibly? It often betrays them by ruining surprise attacks and letting the X-Men know what they're going to do. If I was going to build an army of militarized robots, I would not spend time and money on them having human-like emotions and I would have them communicate with each other silently.