Speech tags for nameless characters

Question

I have a scene where two identical people talking to each other. There is no difference in terms of their physical appearance. The only difference is that one is standing while the other one is leaning against a tree. What is the best way to refer to them in speech tags and narration?

I don't want them to refer to each other by names in the first lines of dialogue as it feels unnatural.

Here is an example:

Two man stood next to a lake. One looked at the horizon while the other one leaned against a tree.
"I know," said one of them.
"Do you?"
"Sure, I saw it myself"
"You did not!"
The one that was leaning against the tree picked up the stone from the ground.

In this example it is not clear who started talking first. Would next example be better?

Two man stood next to a lake. First one looked at the horizon while the second one leaned against a tree.
"I know," first one said.
"Do you?"
"Sure, I saw it myself"
"You did not!"
The second one picked up the stone from the ground.

Is there are better way to write this?

Answer 1

You have two characters that are pretty much completely identical at this point in your narrative, and you are purposely withholding their names from the audience. In such a situation, I would suggest going with your second route and using "first man" and "second man" as your speech tags.

Two men stood next to a lake. The first one looked at the horizon while the second one leaned against a tree.

"I know," the first man said.

"Do you?" replied the second.

"Sure, I saw it myself."

"You did not!" As he said this, the second man picked up a stone from the ground.

Since the men are identical, and the audience doesn't know who they are, you should be very careful to distinguish who's saying what. Unless the men have noticeably different speech patterns, it will be hard to tell otherwise.

I would also like to bring up a point of consideration. Is there any reason why you're purposely being vague with the identity of these characters? You say that you "don't want them to refer to each other by names in the first lines of dialogue as it feels unnatural." In my experience, it may be awkward as a writer to throw in character names into your narrative without a full introduction, but as a reader, I see no issue with it. In fact, pretty much every book I pick up will mention the main character's name within the first lines of dialogue.

So, if it's important that the reader does not know the identity of these two men, go for the "first man," "second man" route. Otherwise, I would suggest just naming them!

Answer 2

You could try to use the few differences there exist. Make them interact with the tree, or look around, or... whatever makes sense for your men. E.g.

Two man stood next to a lake.
"I know", one said, while scanning the horizon.
"Do you"?, replied the other man, leaned against a tree.
"Sure, I saw it myself", his eyes following the fast flight of a kingfisher in the distance.
"You did not!", he took a step away from the tree and picked up the stone from the ground.