The Ray is Fired at..
The petpet lab is similar to the Secret Laboratory as it can alter your petpet. However, you must already have collected the pieces and obtained access to the Secret Lab first. The petpet lab is a great extension of the normal lab, as it isn't all that expensive and you could receive an avatar. Let's look at everything the petpet lab does and decide if you should get it. 
Please realize that changes made to your petpet are immediately undone once you remove the petpet from your pet. That means you cannot sell or trade petpets with lab-made alterations.
How To Get To The PetPet Lab
In order to have access the the petpet lab, you must first have access the the normal secret lab. You must collect all 9 pieces (easily found through random events and thus are fairly inexpensive.) Once you have collected all 9 pieces (shown below), you can place them all into your inventory and visit here. Once you have traded in your map for access to the lab, your map pieces will disappear forever. However, you will always have access to it. If you have access to the lab, you can visit it here.
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What The Ray Does
The ray, when fired at your pet, can do several things.
- Change your petpet's species.
- Change your petpet's color.
- Change both color and species.
- Change your petpet's level.
- Change your petpet's name.
- Turn your petpet into a pile of soot.
- Make your petpet disappear forever.
- Do absolutely nothing at all.
Of those painted colors, the lab can create colors that there are no petpet paintbrushes for. Here are a few of them.
You can also get lab-only species. Here are a few of them.
NOTE: Do not think you can zap petpets in order to then sell them. Not going to happen. If you remove a petpet from your pet it will revert to its original state. You cannot trade zapped petpets. (You can trade them in their normal state, however.) That means though, if you do not like how your petpet turned out, you can always remove and re-attach to go back to normal, or just keep zapping. You can always re-zap unless your petpet disappears.
Should I get the Maps?
I personally think that if you already have the Secret Laboratory, you really should get the petpet one. You probably already have half of the pieces sitting in your safety deposit box! Not to mention you can get a spiffy avatar!
This avatar is only available when the petpet lab changes your petpet into a pile of soot. This is actually one of my favorite avatars.
Afterword
I hope this has helped you learn the "secrets" of the petpetlab. Also note that you MUST have access to the Secret Laboratory before you can access the Petpet Secret Laboratory, regardless if you already have the petpet map.
-Shalane