This paper evaluates persuasion dynamics of animal adoption using text data from a large archive of online pet advertisements. In Study 1, 184,805 adoption profiles from Petfinder indicated how long a pet will remain online and unadopted. Consistent with evidence from related persuasion settings such as peer‐to‐peer lending, pets spent less time online if profile writers had an analytic thinking style and advertisements contained few peripheral processing cues such as social words. Study 2 (N = 676,004 adoption profiles) replicated Study 1 patterns and found that adopted pet profiles contained more markers of analytic thinking and fewer social words than unadopted pet profiles. In an experiment (Study 3, N = 987), participants read an adoption advertisement typical of adopted or unadopted pets. Participants self‐reported that they would be more likely to adopt a pet and visit its shelter after reading a more analytic and less social adoption profile (indicators of adopted pets) than a less analytic and more social profile (indicators of unadopted pets). Finally, Study 4 (N = 3,245 Tweets) demonstrated that more analytic and less social word patterns relate to increased engagement online, such as likes and retweets. These data suggest pet adoption that begins online is a social and psychological process, enhanced by messages with markers of complex thinking and few humanizing references. Advances to persuasion theory are discussed, underscored by the implications for pet adoption and how language patterns in online advertisements can reflect influence at scale.