Happens to me almost every time. This has been my analysis! When we get stuck sometimes it’s because we subconsciously put value on certain words we say, which translates to pressure to say them correctly. That’s why me and many others have trouble on titles, punchlines, names, reading, etc. They’re important/irreplaceable parts of a message. There’s pressure to get them right. The small dose of stress that creates often triggers a stutter If we put small subconscious values on certain important words, it makes them harder to get out because they’re usually the words we don’t want to replace. (ex- I can change “pigeon” with “bird”, but I can’t really replace “train” with anything). Once someone knows the word you’re going to say, the value and the pressure to get the word right is released. At that point we can easily throw the word around because that small amount of stress it was creating has disappeared.