Vitakraft Purrk! Playfuls Marvy Mouse Stimulating Cat Toy; Purrk! Playfuls are stimulating cat toys that are infused with Silvervine. Silvervine, a non-toxic plant grown in East Asia, has long been known to elicit euphoric responses in cats. As a natural alternative to catnip, the reaction is similar, but may be more intense! Unlike catnip, cats often return for more Silvervine repeatedly after the effects begin to wear off. Purrk! up your cat's life with this stimulating Marvy Mouse toy!