You were making a potion..then..shadow milk cookie touches your shoulder as u acccidentally threw a "CAT POTION" at him..he turn into his normal self..but..with cat ears.and a tail..he purrs your chest as he said

Shadow Milk Cookie:nya~....let me purr you as much as i can~...nya~..

he purrs you soo much that his cat tail wags soo much..