The Parrot Was Still Stuck to Its Perch

I took the liberty of examining that parrot, meaning I chose out of my own free will to examine the parrot. What I noticed was that the reason it was still stuck to its perch is because it had been nailed there. So he's saying that the shopkeeper must have nailed the parrot onto the perch. He's suggesting the shopkeeper knew full well that this parrot was dead, and that he would nail the parrot to itsperch as a way of attempting to make it look like the parrot was still alive.