POP! That is what happens when you open the door.
Step 1: Stuff You Need: Pin, Popsicle Stick, Tape and Balloon.
Step 2: Build
Tape popsicle stick to pin.(like in picture)
Step 3: Build
tape stick with pin on to top of door .(like in picture)
Step 4: Build
tape to wall.(like in picture)
Step 5: Done!
now wait for some one to walk in the door and POW!!!!!!!