If you prick yourself with the needle, it's going to hurt.
ーIf you get poked with the needle, it will hurt.
「針が刺さったら痛いよ」
to get poked with the needle で「針が刺さる」
hurt で「痛む」
ーIf you prick yourself with the needle, it's going to hurt.
「針が刺さったら痛いよ」
to prick yourself with the needle で「針が刺さる」
ご参考まで!