Generously grease a 11x7 inch tray with some butter/margarine. Set aside.
In a large pan, melt your butter/margarine over a low heat.
Add your marshmallows to your pan and allow them to melt, stirring occasionally to avoid them burning and sticking.
Once your marshmallows have completely melted, add your food colouring and mix through. Remove from the heat and add your rice crispies.
Mix in your rice crispies as quick as possible, before transferring the mixture to your prepared tray. The mixture will be sticky, so work fast. Using the back of a spoon, press the mixture into the tin - greasing the spoon in a little excess butter/margarine will also stop the mixture sticking.
Allow your rice crispy squares to set for a couple of hours. Once set, cut to your desired size. Have a sheet of greaseproof paper to hand for decorating also.
Melt the chocolate over a bain marie, or in short bursts in a microwave. Dip your rice crispy squares into the chocolate, letting the excess chocolate drip off, before transferring to your piece of greaseproof paper.
Using a little dab of chocolate, stick the edible eyes onto your rice crispy square. Add a mouth and any additional features by drizzling a little chocolate with a small spoon or a cocktail stick.
Allow the chocolate to set completely before enjoying.