So many people knocking on your doors it must be truly frustrating ;)
The concept here is based on connected speech with future simple (will). I pay huge attention to this area when I teach my students. What is this joke about?
Church will be the best place.... -> church'll -> Churchill
Normally, only the pronouns (I, you, he, she, it etc) are contracted, as shortening all words with will would make them very difficult to pronounce.
However! these are knock knock jokes and the purpose of such is to make people laugh (or in this case learn something as well).
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