The last April Fool's day my friends and I played the following trick on our friend: at night, when our "victim" was sleeping, we pasted the doorway of her apartment from the outside with wall-paper. The paper had picture of bricked wall. So, when the "victim" opened the door she was struck dumb... Immured... Of course, in some seconds she understood that it was just wall-paper, but at first her reaction, judging from her words, was real shock and misunderstanding...
So, I think you could repeat this experience, if your liked the idea!