Cross between a cat hissing and a fish, basically a fish hissing.
Me: walks up to fish tank
Fish: hissssssssssh
Me: *calls vet* Is that normal?
Vet: No bring ur fish 2 me immediately
Me: *brings fish 2 vet*
Vet: ur fish swallowed a cat we will do surgery
Me: so that explains why A. my cat disappeared and B. why my fish suddenly got so fat