We see a monkey in a cage eating a Kit Kat and drinking a can of coke.
We see a man in a white coat and clipboard observing it.
We see three men in suits approaching.
SUIT
"How's the experiment going Johnson?"
JOHNSON
"We haven't started yet sir, he's having his lunch"
I like that, maybe could just see the monkey snorting a line of coke
Johnson says "We haven't started yet sir, he is having a line"
Alternative
We see a monkey in a cage eating a Twix and drinking a can of coke.
We see a man in a white coat and clipboard observing it.
We see three men in suits approaching.
SUIT
"How's the experiment going Johnson?"
JOHNSON
(Winks)
"We haven't started yet sir, he's having his lunch"
Johnson then pulls off a white sheet and we see an electric chair and a table full of hypodermic needles,pliers and metal bowls.
The monkey sees this and starts choking then falls to the floor of the cage.
Johnson then looks at his watch and writes on his clipboard as he speaks
JOHNSON
"3 minutes again sir, they seem to choke quicker on 'Twix' and slower on 'Creme eggs"
SUIT
"Excellent, keep up the good work"
Funny
I liked the original better - quick and funny. (less is definitely more)
Really nice idea. 
Perhaps you could go for a classic piece of animal testing to wrong foot the audience even more:
[A BEAGLE is smoking a cigarette in a laboratory cage]
SCIENTIST 1: How's the experiment going?
SCIENTIST 2: Give us 5 minutes, he's on his break.
Now that works on its own, I can take no credit for that one and it's better than mine by a kilometer (I went metric on Tuesday)
Well, that's very kind, Teddy, but I'd say it's definitely still your joke, I just gave it a shave and a trim before sending it out into the world.