 Toward the end of the whole sequence with Scully in the beginning  trying to find information on where Mulder is, she is running out of  Fowley and Spenders office and going around the corner toward the  elevator. She slips and almost falls. Its quite obvious, you can  hear her slip and also see Gillian Andersons arm shoot out to catch  herself. Shes quite lucky that she didnt fall because if she had,  since they filmed the entire episode in real time, they would have  had to start back at the very beginning of that scene and done it  all over again.