alight upon appear unexpectedly arrive at arrive upon be unexpected blunder upon bob up bump into chance upon come across come among come at come on come unawares come up against confront creep up on discover serendipitously encounter fall across fall among fall foul of fall in with fall upon flash upon one get at happen upon hit upon light upon meet meet head-on meet up with meet with pitch upon pop up pounce upon reach run across run into run smack into run up against run upon strike upon stumble on stumble upon tumble on turn up