WP7Connect just posted an interview with the AmusedSloth team.

Here’s an excerpt

How did the concept for ‘chickens can’t fly’ come about?
At its inception, it was a very different design, set in a sci-fi world on a deserted planet (as you can see in the first concept art…). The core theme remained the same though: fall down through a series of tunnels, with little hope of slowing down, and avoid as many deadly obstacles as you can.

One of our developers kept joking about including a chicken in the game as an Easter-egg. When we let ourselves go wild with ideas for obstacles and power-ups it soon became clear …

You can read it in its entirety here: Dev Inside Look.