Simple(ish) question

Simple(ish) question is it rude to say the word that someone is trying to say? example: someone is ordering food and im the one taking the order, and they are asking for ketchup, but are stuttering on the word ketchup. if i know they are going to say ketchup in a couple seconds, would it be rude to interject their stutter and ask "ketchup?" and they nod. ive always wondered this so i usually stay silent until they get the word out. just wanted to ask this community on your opinions or experiences on this