They don't do that anymore because the original sound effect was stolen from Messiah and Tommy Tallarico sued after ROBLOX refused to pay him for the rights.
This question confused me for a bit. I know what vore is, I am passingly aware of Roblox, but I didn't know what an "oof" was until I read an article about it on Roblox Wikia.
In order to answer this question, I think we will need more information:
Are you voring a Roblox man in Roblox, or in real life?
If you are voring a Roblox man in Roblox, which Roblox place are you doing the vore in?
If you voring a Roblox man in real life, are you voring a tulpa, or a physical object (e.g. a Roblox-themed action figure)?
The novel version of The Hunger Games had this scene where a girl's head gets smashed in with a rock and she lies on the ground making weird, guttural, unnatural moaning sounds for like two minutes before the cannon fires to announce her death.
Immediately upon hitting your stomach. There’s a cylindrical kill volume programmed around your stomach that sets HP to 0 on contact with any other entity. This is actually a really convenient way to do this both for the devs and for speed runners as all you have to do is jump backwards and slightly to the right in to any NPC and if you animation cancel exactly half way through your stomach kill volume will clip out of your body and touch the NPC, killing them instantly. Use this knowledge to great effect. I believe in you.