What is the murderer doing to inspire this? I imagine a melodramatic old school mustache twirler with a cape – the kind who ties damsels to railroad tracks and he’s making various evil expressions, warming up to do his evil business.
It makes me think of one of the opening scenes of The Imposters when Stanley Tucci and Oliver Platt are practicing acting in their bedroom. One gives the other an emotion and the other makes the face of that emotion. I imagine that this murderer in the Mousetrap is cycling through his villain faces just as those actors do in that scene.
The Hamlet Project 
I never really comprehended this line or how hilarious it could be when played until I saw the Jacobi version, now on Amaz*n instant — Jacobi and his Lucianus had me in stitches and I had to rewind it about ten times. Now I feel cheated when I see a version that doesn’t similarly play it for laughs.