One mailing list article today forced me to find a way to skim through all the thread.
`A T` (`gnus-summary-refer-thread`) fetches all articles in the current thread.
`M-s M-s` (`gnus-summary-search-article-forward`) performs a regexp search forward.
Use `M-s M-r` for backward search.
The search is done once after hitting `RET`. To repeat it, use `M-S` (forward) or `M-R` (backward).
#RTFM
(info "(gnus) Finding the Parent")
(info "(gnus) Searching for Articles")