I can see it's a tricky decision. Bell wasn't the only failure, Cook is under pressure and Prior didn't bat like a top six batsman in the first Test either, and shortening the batting line-up will increase the pressure on both. But I think it's got to be done. If there's going to be swing in the air there's a strong argument for bringing in Sidebottom as your fifth bowler, but that'd be a bigger risk than I think they'll be willing to take. I'd play Wright, though it does run the risk of falling between two stools and getting another Gavin Hamilton.
Got to bear in mind as well that South Africa's bowling line-up is going to be stronger than last time as well, Steyn will probably return and Kallis will be back to bowling duties. Their difficulty is who to drop to make way for Steyn - by rights it ought to be Ntini, who has looked past his best for a year or so now, and de Wet had a good debut. But that's not an easy decision for them to make either, not least for political reasons.