Julian Nyarko, an associate professor at Stanford Law School, said the legal test for agreement to a contract centers on how a reasonable person would interpret the signs that both parties gave. In some cases, a verbal agreement is sufficient, he said. “For most intents and purposes, a reasonable person, if they see a thumbs-up emoji, would think that the person who is giving the thumbs-up wants the contract,” Professor Nyarko said. “It fits quite neatly into the legal doctrine that the courts have established.”