Dead or hunt dead. I also use the command for treats. I start out using it with hotdog training.
This is a great point to the OP. I've had much better luck over the years training "dead" with treats, etc than I have with bird scent on dummies, not to mention it's way cheaper! You are essentially training the dog to "search" for something
... once they associate the command "dead" with finding something good with their nose, they hone right in on it regardless of what it is.
I can drop a Cheeto on the floor in the kitchen and call my dog in and tell him dead and he'll search the entire kitchen until he finds it. I can also ask him where his ball is and tell him "dead" and he will scour the backyard until he finds it. If we are hunting birds... that's what he finds.
Make it a game with the pup.