Det mycket korta svaret är att de tittade på sina fötter (på den tappla repet) snarare än att titta framåt.
DukanskeocksåvillnoteraattävennågrasekunderinnandekomtillslutetavbronvarMolaRamochhanshantlangareingenstansattse:
Filmens officiella filmbindningsversion nämner inte specifikt hur Willie och Short Round gick in i fälla men det påpekar att Indy var för engagerad med att titta ner (se till att han träffar plankorna och undvika de saknade) att märka vakterna som kommer ut ur skogen vid slutet av bron tills det var för sent:
He walked quickly, hanging on to the twine rails. Every few steps his boot would break through; he’d have to catch himself on these upper ropes. Consequently, he kept his eyes turned downward most of the way, looking to step over the weak boards. When he was nearing the middle, he heard shouting ahead. He looked up to see temple guards appear at the far end of the bridge.
Willie and Short Round were caught as soon as they stepped onto hard ground. They struggled with their captors, but it was futile. There were too many.