Finding the Relationship
The fastest lever in a cold read: who these two people are to each other.
Give two actors the same page and one decides she is talking to her estranged father while the other decides he is talking to a coworker he barely knows, and you will watch two completely different scenes. The words did not change. The relationship did. This is why the relationship is the single most efficient choice you can make in a cold read. It costs you one decision and it colors every line on the page. When the clock is short, it is the lever to pull first, because it does more work than anything else you could spend the time on.
Why it changes everything
How you ask someone for money depends entirely on whether they are your brother, your boss, or a stranger. How you deliver bad news depends on whether the person on the other end is someone you love or someone you are afraid of. The relationship sets the stakes, the manners, the history, and the permission. It tells you what you are allowed to say directly and what you have to dance around. Decide it, and a flat line like "I need to talk to you" arrives loaded, because the audience can feel the years behind it.
The opposite is also true. Skip the relationship and every line comes out at the same neutral temperature, polite and unplaced, which is exactly the read casting forgets the moment you leave.
How to find it fast
The side usually tells you, if you read for it. Look at how the characters address each other, what they assume the other person already knows, and what goes unsaid. People who share a history do not explain themselves; people who just met over-explain. Sharp jokes, old grievances, casual cruelty, and shorthand all signal intimacy. Formality and careful phrasing signal distance.
If the page is ambiguous, and cold sides often are, you get to choose, and you should choose the version with the most heat. Between "these two are acquaintances" and "these two used to be married," pick the marriage every time, as long as the lines can support it. The more loaded relationship gives you more to play and reads as a braver, more specific actor. You are not contradicting the text; you are filling a gap the text left open, which is your job in a cold read.
Make it personal, not abstract
"They are siblings" is a label, not a relationship. What plays is the specific texture: he is the younger brother who never got out from under the older one's shadow, and he is asking for help he resents needing. Push your choice one layer past the category into something with a wound or a want in it. You do not need a backstory novel. You need one specific thing that is true between these two people right now, the thing that makes this conversation cost something.
That specificity is also what feeds making choices under pressure: once you know exactly who this person is to you, the choice about how to play the scene almost makes itself.
Play it to a real person
A relationship only exists between two people, which means it only comes alive when you play it to the reader instead of reciting at the page. Let the way you look at them carry the history. Hold the relationship in your eyes when you land a line, the way staying off the page lays out. The most useful rehearsal for this is reading unfamiliar sides to a reader who answers back, so you are relating to someone rather than to paper. A reader inside Memorlined will run the opposite lines while you rehearse deciding, fast, exactly who you are talking to. Decide that well and half the cold read is already done.