After pushing the buzzsaw abandon of their earliest records to its logical extreme on the masterful No Pocky for Kitty, Superchunk begins reinventing itself with their third full-length, On the Mouth, a record as invigorating as it is frustrating. Without sacrificing any of the energy or conviction of past efforts, many of the disc's 13 songs harness Mac McCaughan's breathless pop-punk melodies into tighter, more demanding contexts -- highlights, like the singles "Mower" and "The Question Is How Fast," introduce a new arsenal of shifting rhythms and explosively tense dynamics which reveal unexpectedly limitless possibilities within the classic Superchunk approach. The problem is that On the Mouth equates to something less than the sum of its parts -- while tracks like the blistering "From the Curve" and "Package Thief" barrel forth with the sheer recklessness of old, their adherence to the band's past makes for an ill-fitting match alongside the album's more ambitious moments. More problematic, the slow, plodding "Swallow That" -- while an admirable departure from the norm -- is simply tedious. Still, more often than not On the Mouth comes up with the goods, and remains a pivotal turning point in Superchunk's continued evolution.