How do I get my my pet walrus to eat my little sister?

I have a pet walrus named Sammy. My little sister is really annoying, so I want Sammy to eat her. My best friend said that if I pour fish oil on my sister while she is sleeping, I can get Sammy to sneak into her room and bite her head off. This is ideal, because I don't want my parents to hear the screams. I also want to prevent the spilling of blood all over our carpet (my dad doesn't like blood on his carpet), and I don't want her room to smell like fish oil (that's too obvious). Also, my sister carries a machete underneath her pillow, and I don't want her to stab Sammy in the neck again. She already did once when Sammy tried to poop on her Barbie doll, and I don't want Sammy to have to get more stitches. Oh, and Sammy is afraid of penguins if that helps.