There is a need to appear intelligent and make the farmer appreciate it. If all you act as is a beast there is no reason to maintain you as you are and not get you brainwashed. The idea is to appeal to him as a tool or way to implement his will while making him understand and appreciate that something intelligent is more useful than a beast of burden. If he questions why I would serve and not turn on him, there is simply no reason to. As a dragon I will outlive him and likely by more than a couple hundred years so spending 60-100 years honoring my bargain is roughly the equivalent of helping out around the house as you would when you are a child. If he seems offended by the fact that I will outlive him I would point out that so would his children and that my situation isn't one of looking down on him just that I was born later and can't help that I will likely outlive him. If after I hatch I can take human form I would try to as much as possible around the farmer and the family if I am revealed to them as well. "The unfortunate reality is that like your other children, I will outlive you. More so, by more than a few years or decades. Due to the nature of my species honoring my deal with you is comparable to your daughter and second son helping around the farm as needed until they are married off or set off to find their own way. It is only natural for a child to help their parent(s) while they are young and dependent on them, is it not?" Something like that.