>>115972If you're wearing a kigurumi mask, it's kind of like you're talking and hearing with a box over your head, or a motorcycle helmet.
It can vary wildly how big of an effect it has though depending on the mask's design. Like if it has an more open or closed mouth, and the amount of padding in the ear or mouth area and such.
You can roughly simulate this effect by speaking with your hand over your mouth or listening while covering your ears. It becomes a bit muted and also echoing your own internal voice a bit more.
That itself might not be that much of an issue, but it compounds if both are wearing a mask, meaning it could easily start to become unclear what the other is saying. This is another reason why someone in a kigurumi cosplay might prefer not to speak at all and do gestures or write instead.
Also, this is just from things i've heard. I don't really know it that well...