Spitting on stairs

The other day we were walking down the street and witnessed a lady trip while she was walking up some stairs. She looked a little flustered, stood there and straightened herself out, then kept going. She suddenly stopped, turned partially around and glared at the stairs, and then began to walk away again. Then she whirled around and walked briskly backed to the steps, leaned over them and appeared to say something, and to our surprise, she spit on them! Smiling, she turned around and walked away.
We think it has to do with the general belief in spirits, the evil eye, negative influences, etc., and she was expressing displeasure to whatever was in the stairs that made her trip.