The Spiked Collar (DS).
The Spiked Collar appears in both Nintendogs and Nintendogs + Cats as an accessory your puppy can wear. In Nintendogs, it is a black, presumably leather collar with large silver spikes sticking out of it and square and circular studs. In Nintendogs + Cats, there are two versions, black and red. They are both the same as the original Nintendogs Spiked Collar, only different colors.
Gallery
Shiba Inu wearing the Red Spiked Collar (3DS).
A Dalmatian puppy wearing the spiked collar in the DS version.