Over here I buy all my shellfish on the hoof, as it were. I used to do the 'throwing them in the in the boiling water trick' but the cowards kept jumping out and I would have to chase them around the kitchen. I tried clamping them down in cold water and bringing it up to the boil on the basis that they went to sleep and didn't feel anything but this made them too tough. Final success was throwing them in fresh water. For some reason they quietly croak after an hour or so and then they are ready for boiling.