$ perl -00 -wnl -e '/\S+ OBJECT-TYPE/ and print;' mib.txt  | perl -00  -wnl -e '/(".*")/s and print $1;'
"The number of received packets that are either undersized,
                oversized, or have FCS errors."

"The number of received packets that are either undersized,
                oversized, or have FCS errors."