Can breath shape a space?
People with bigger lungs create a bigger space. Two persons encountering can be seen as a fight on personal space. The closer the other gets the more limited you are in space.

What if the space is encoutering you, being defensive at certain spots? Doors that will be blocked, narrow spaces where you will be pushed out and steers you in another direction.

The staircase as a defensive system is the ultimate place to disturb people in there movement. It slowly grows underneath the staircase and reveals itself after a while. When fully grown it prevents people from going up or down. They will be forced to stay where they are. Waiting until the defensive system will get shrunken to a vulnerable point and be easier to pass.