Zero Hippopotamuses

Image Source: hippopotamuses.org

Zero is plural.

Really. Try it with me now.

(2) Two hippopotami have soiled the carpet in my den.

(1) I have a hippopotamus in my powder room.

(0) There aren't any hippopotamuses in the kitchen.

(0) On close inspection, I found zero hippopotami in the dishwasher.

When programming I have to test before composing sentences:

IF ABS(countVariable) = 1 THEN
     textVariable = "hippopotamus"
ELSE
     textVariable = "hippopotamuses"
END IF

I know you're wondering. The preferred plural of hippopotamus is hippopotamuses, though hippopotami is accepted in the Oxford English Dictionary. Source: Wikipedia

Of course when encountering hippos in your dishwasher, I believe it would be correct to simply exclaim, "Snakes on a plane!"