I've been thinking about telling my sister that Teletubbies are hiding under her bed.
What is your reasoning for telling her something is hiding under her bed?
She's so gullible, I know she believes me.
You shouldn't play pranks on others if it triggers their fear. Although pranks can be done in fun, they can also go too far. Be sure the person you're playing the prank on is okay with jokes.
Are you pranking me?
No, I'm not pranking you and I'm being real when I ask you to not do this, as it can genuinely scare your sister. You don't want to be responsible for your sister being afraid of sleeping and you should be sensitive towards her.