A Vibra-Slap looks something like this:
 #;,.                                        
 -  ##                                       
 ;   .                                       
 /   M-                                      
 =   @                                       
 #   :                                       
 :   =                                       
 ;   =                                       
 ;                                           
 /   .                                       
 :    :                                      
 :   .%                                      
 ;   .X                                      
 :    #                                      
 :    #                                      
 ;    M                            $%%H+M    
 ;    M                           @X%/$MHH   
 :    @                          @@+;;;HMMH  
 /                               M@/:;@MM##  
 /     ,#M####################MM@MMM%$M#M##  
 ;        .,.,,,=-/::==:::;+%$%+M##########  
.;                               #########M  
                                 ##########  
                                  #######M   
 %#                                #####-    
    #                                        
    M.#                                      
        #                                    
        @ M                                  
          M@$                                
            ; #                              
              %M#     ###-                   
                =#, #######M;                
                  H:M###########M            
                    ;######M####M###         
                    ++##############M##-     
                   ./%/:############M####    
                    %+//=M#M#############    
                     /X+/=#M#############    
                      M+/;;######M#######    
                       #++;+########M####    
                        @+;;/M####M#/#M#H    
                         #;=;M#########      
                          %;;M#######+       
                           #;MM#####         
                             M#%      

That's at an angle. The Vibra-Slap shown here is really upside down. The weight is at the top and the bell is at the bottom. The bell has rib-like rows of metal in it that create the "rattlesnake" sound.

What's very important to your Vibra-Slap is that you keep the screw behind the bell very tight or it might not make any sound at all. Also, never hit the bell, only hit the weight. Hitting the bell can damage the Vibra-Slap. I learned this the hard way while trying to play a Vibra-Slap, a cowbell, a shaker, and a hi-hat at the same time.

The new interesting thing is that the Vibra-Slap is now in version 2.0, and you can currently research the "Vibra-Slap II" at the manufacturer's (LP) website: http://www.lpmusic.com/Product_Showcase/Sound_Effects/lp_vibraslaps_II.html