Explanation: "Behold, dog" and variations are an Elden Ring meme based around the simple form of communication players can make with each other (using a limited list of vocabulary and grammar) not including 'tortoise', despite there being prominent tortoises in game. Yet, 'dog' is there. So it became an in-joke to refer to all in-game tortoises as 'dog'.
The Testudo formation, depicted, is a Roman formation where the soldiers lock their shields together to provide cover nearly impenetrable from arrows and other projectiles. It's very famous, I'm sure most of you have seen depictions before - hardly any Roman media goes without it. 'Testudo', however, is Latin for tortoise.
Therefore
Behold
dog