# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/[^.?!]*(?<=[.?\s!])flung(?=[\s.?!])[^.?!]*[.?!]//igm;t' <<< "As she did so, a most extraordinary thing happened. The bed-clothes gathered themselves together, leapt up suddenly into a sort of peak, and then jumped headlong over the bottom rail. It was exactly as if a hand had clutched them in the centre and flung them aside. Immediately after, ........."
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html