Some of those voicelines are restricted to being heard only by the one being sucked - if you don’t or only very rarely get sucked and/also that state gets removed very quickly, you won’t hear them. So, my advice for hearing them: suck more to get sucked more.
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Further, the ‘being incapacitated’ sound is way overtuned, so the actual Leech line gets overshadowed by it.
Yeah most of those lines sound like they are from V1, i remember some of them. Maybe they were ported into game 2 without being integrated (on purpose)?