Variables. Here's the events you need to change/add.
0 OnActivate > Player > VCE_ifVariable > [trap] [==] [1]
ADD OnVariableFalse > Self > VCE_modVariable > [Player] [trap] [Set] [1]
ADD OnVariableFalse > Self > ContentStart > [Unrestricted] [CW]
ADD OnVariableTrue > Client > CenterPrint > [\c6YOU'RE TRAPPED!]