Duck, duck, goose!

Operation Flashpoint scripting language, 48 bytes

f={s="duck\n";s+([s,""]select random 1)+"goose"}

Always prints either one or two ducks.

random 1 returns a (floating point) number between 0 and 1. That number is passed as an argument to select along with the array [s,""]. The random number is then rounded to the nearest integer (either 0 or 1), and the array element at that index is selected from the array.

Call with:

hint call f

Output:

Alternative 56 bytes version:

f={s="duck\n";format[s+"%1goose",[s,""]select random 1]}

World of Warcraft 81 Bytes

Here's a macro that you can run in World of Warcraft.

/run for x=1,random(1,9) do SendChatMessage("Duck") end; SendChatMessage("Goose")

Minecraft <1.13, 72 54 bytes

Sorry, I had to.

Instructions:

• Create a new Minecraft world in Creative Mode
• Find the save folder for that world, and place the following code in data/functions/minecraft/ddg.mcfunction
• Run /function ddg in the game console

How it works:

Outputs the word "duck" for every entity in the world, then outputs the word "goose". Since entities are constantly spawning and despawning, the number of "duck"s will not be consistent. I used tellraw instead of the much shorter say because say outputs the name of the entity, while tellraw outputs exactly what it is told.

execute @e ~ ~ ~ tellraw @a "duck"
tellraw @a "goose"

Screenshot

Edit: Changed {"text":"duck"} to just "duck" (and the same with "goose")