Do you play World of Warcraft?
If not then yeah, you wouldn't get it
Tank AKA meatshield, the class that will take the most damage to keep every else alive.
Lock =Warlock
Heels (heals) a healing class -paladin, priest, druid, shaman
Shammy = Shaman
Its a World of Warcraft reference. Lock and Tank, Warlock and Tank class (maybe warrior, paladin, et-cetera.
Heelz and a shammy also refer to other playable classes in the game, although the cat seems to think they are high heals and a sham-wow. ROFL. Pretty funny when you get the references.
Thats kinda how i think Milo, Ollie and Shadow see Dave and I when we talk about WoW.
"Shammy... Why does mommy want one? I didn't pee on the floor, did you?" Milo looks at Ollie, cluelessly.