Assuming the corpse-zombie moves faster than a shamble...

Natasha, Clint and Tony, after taking a long second to kind of just stare at the monster like really, is that a zombie, are we hallucinating - take off to try and avoid the monster. Unfortunately, as they're running, Natasha stumbles and falls. Clint, ever the well-meaning moron, doubles back to help her up and manages to shove her standing and out of the way long enough for Mr. Corpse Friend to grab Clint instead. Today, Clint is the weakest link sacrifice.

That'll teach them for trying to write a virus, huh.