That is true. They are definitely rational

Detective Del Spooner:
[entering Calvin's office room]
In the lab, before Sonny jumped us... Susan Calvin:
[interrupts]
Sonny? Detective Del Spooner:
The robot. Susan Calvin:
Your calling The robot Sonny? Detective Del Spooner:
No, it did. The robot did. I didn't care, The robot said it was Sonny. In the lab, there was a cott. I'm asking you, did you see the cott? Susan Calvin:
I've slept in my office. Detective Del Spooner:
I went to Dr. Lanning's home, it looked like he hasn't been in there in weeks, and I saw that same survailence strip on the ceiling. Susan Calvin:
Lanning had his home security system linked to USR. It made his life more convenient. Detective Del Spooner:
Maybe, maybe someone in USR was using those systems to watch him. Maybe even, keep him prisoner. Susan Calvin:
What are you talking about, who? Detective Del Spooner:
Maybe Lanning was onto something. Maybe, there's a bigger problem with The robots, and Robertson is trying to cover it up. Susan Calvin:
Humoring you for no reason, why? Detective Del Spooner:
[becoming annoyed]
The same old why, how much money is there in robots? All I know is, that poor old man was in trouble, and I'm sick and tired of doing this shit by myself. You're on the inside, and you're going to help me find out what is wrong with these robots. Susan Calvin:
[not believing a word Spooner is saying]
You "want" something to be wrong with them. This is a personal vendetta. Detective Del Spooner:
You're putting me on the couch? Alright. [sits on the desk chair] Susan Calvin:
One defected machine is not enough for you. You need them all to be bad. You don?t care about doctor Lanning's death. This is about, The robots and, for whatever reason you hate them so much. Detective Del Spooner:
[gets up from the chair]
Well, let's see. One of them put a gun in my face, another tore a building down with me still inside. Susan Calvin:
[checks her robot monitor device]
Demolition was schedualed for 8 PM this evening. Detective Del Spooner:
It was 8 AM tomorrow, and I don't give a shit what that thing says. Susan Calvin:
You are burdening on non-clinical paranoia. Detective Del Spooner:
[getting angry, but trying to remain calm]
You are the "dumbest" smart person, I have ever met in my life! What makes your robots so perfect? What makes them so much... goddamn better than human beings? Susan Calvin:
[snapping back]
Well, they're not irrational or... potentially homicidal maniacs for starters! Susan Calvin:
[sarcastically]
That is true. They are definitely rational