I always avoid .swf files just for that reason...... Don't even know what an .swf is, but 9 times out of 10 its a face that pops out and an loud scream
.swf is the file extension for files made from macromedia flash...somewhat a multimedia product...
many are really fond of making those "mysterious songs/ games where something unexpected pops out"....(not so good for anyone with weak hearts)...hehe
This is the kind of thing that is a cruel and terrible prank when someone sends it to you, but is absolutely hilarious when you send it to all your friends.