I'll put a girdle round about the earth in forty minutes.
You can either interpret that as meaning it will take him forty minutes to go around the earth, or that forty minutes from now he will put a girdle round about the earth.
What kind of ambiguity is this? I think it's lexical, because it does rather depend upon the meaning of "in".
I don't think I could get any dorkier, but you never know. :-)