So-called Wizard-of-Oz (WOZ) simulations are a popular framework for investigating the nature of human machine interaction in general and for the development and evaluation of designs for spoken dialog systems in particular. In this paper a WOZ simulation of a speech based ticket reservation system is presented. In contrast to most of the studies performed in this framework we are not concerned with the evaluation of different dialogue designs. In our experiment the WOZ frequently rejected or misrecognised user utterances. The findings on the prosodic properties of repeats and corrections triggered by these recognition errors are presented. In addition some data on the lexical content of the user utterances is discussed.