Read the following article and answer the question.

We were out the door according to schedule and even the Sunday drivers could n't keep us from getting to the cinema on time . We bought our tickets , purchased some snacks , and went in to get seats . When we opened the door to Theatre 2 , the unmistakable smell of urine slapped us in the face .

How can urine " slap " ?
The smell makes you gasp / gag .