The actress appeared alongside her 'Dune 2' costars Sunday in Sao Paolo for an event called CCXP 2023 -- basically just a Comic Con thing, where they all showed up alongside director Denis Villeneuve and talked about the forthcoming sequel in front of fans.

As their segment was coming to a close ... the entire cast -- including Timothee Chalamet, Zendaya and Austin Butler -- gathered toward the front of the stage to pose together.

Out of nowhere, this thing comes flying in from the audience and smacks Pugh in the mug -- which definitely caught her by surprise ... not to mention everyone else too. All her cast members checked on her to make sure she was okay ... and their time ended awkwardly.

No telling what exactly it was ... but at first glance, one might say it resembles a shrimp.

Unclear if anybody was held to account over this -- if you watch the video, it doesn't look like security is running over to the culprit ... or if much of anything else was done at all. Of course, it goes without saying ... this troubling trend of hurling objects continues even now.

We've seen a lot of performers -- especially musicians -- have to deal with overzealous fans like this here in the States ... but it appears people all over the world are doing it as well.