I was watching "The Big Bang theory" S7 E9. And I couldn't understand the meaning of "tip a cow". Please also explain the remaining conversation too. I am an Asian and not good at English. Here is the full conversation:


> Leonard: The math is all there. It's not real. 
>
> Penny: Yes, it is.
>
> Sheldon: Yeah... uh, look. It is scientifically impossible for a person to tip a cow. Even you, with your stocky build and lumberjack shoulders, you couldn't do it. 
>
> Raj: It's horrible. Why would you push a cow over? They're sacred. 
>
> Penny: Oh, stop it. I've seen you eat, like, a million hamburgers. 
>
> Raj: Hey, an animal can be both sacred and delicious. 
>
> Penny: Look, I'm telling you I've done it, okay? I clearly remember the cow standing up and then the cow on its side. 
>
> Leonard: Were you drunk? 
>
> Penny: I was 16 in Nebraska. What do you think?
>
> Leonard: I think you're the one who fell over. 
>
> Penny: That would explain why the sky was also on its side.