#1: Wait until (preferably jumpy) acquaintance leaves the room
#2: Set this as their wallpaper
#3: Turn off their monitor
#4: Wait for them to come back
#5: Surprise obtained

Inkerius said:
#1: Wait until (preferably jumpy) acquaintance leaves the room
#2: Set this as their wallpaper
#3: Turn off their monitor
#4: Wait for them to come back
#5: Surprise obtained
#6: ???
#7: PROFIT!!!!

this is a new level of surprise

I can't say that I wasn't surprised.

Now all I need is an iPhone version...