This ability is part of what lets Nick Fury and company escape the attacking Kree, but it also means that when Fury got scratched, it wasn’t a simple cat scratch, it was alien creature scratch and who the hell knows what bacteria that thing was carrying?
Goose is an alien creature that looks like a cat on the outside, but is capable of extending multiple octopus like tentacles from its mouth that are able to do some serious damage.
Of course, I sort of buried the lede up there (in an attempt to not put spoilers too early in this) because the fact is Goose the cat isn’t really Goose the cat.