Figure 1.1 Body parts that contribute to canine visual communication.

      Source: Illustration created by and used with permission of Natalya Zahn.

Dog size and postural movements are observed by dogs and people alike. Unlike body size, posture can be modified to expand or contract, the former suggesting confidence or alertness and the latter conveying fear, prevention or reduction of conflict, or affiliation (Schenkel 1967). Dogs reduce size in multiple contexts and with different communicative meanings. A dog lying on the back in “passive submission,” often with ears back, tail tucked, and the inguinal region exposed, deescalates conflict and inhibits attack. Dogs can also display a more inviting “belly‐up” posture to solicit a belly rub. Alternatively, “active submission” may not be motivated by deference or a response to threat (Bradshaw and Rooney 2017). Instead, approach with low posture, low wag, and muzzle (or mouth) licking is an affiliative display to gain food, greet, or maintain or restore social bonds.

      In interspecific contexts—such as if a dog has done something an owner deems wrong— submissive displays can be misinterpreted as a dog’s knowledge of wrongdoing. Instead, behaviors such as freezing, approaching or retreating with a depressed posture, low and quick wagging, ears back, or rolling onto the back or lifting a paw are best viewed along ethological lines as cohesive displays and non‐threatening appeasement postures to keep the group together. Research finds these behaviors are not indicative of a dog’s “knowledge” of misdeed or an admission of guilt (Horowitz 2009a).

      Dog body posture can encourage “coming closer” (distance between individuals decreasing) or “backing up” (distance between individuals increasing), and a dog's body‐weight distribution offers subtle yet valuable information. A dog with weight shifted forward and upper body pressed over the front legs shows forward momentum, interest, confidence, or alertness. If a dog leans forward toward another dog—and the receiver leans back, looks away, or moves away—the second is engaging in conflict avoidance or communicating the dog’s desire to avoid closer interaction. If signals go unheeded, dogs may resort to defensive aggression over time and even fade out the use of distance‐increasing signals.

      Limbs are central to body‐weight distribution and dog movement. While people may take note of limbs in the context of parlor tricks like “high five” or “give paw,” these gestures bear no social meaning for dogs apart from possible food reward or human praise. Instead, “offering a paw” is a submissive or appeasing display and, for example, may be performed in response to an upset owner. Sweating paws could indicate acute stress, but these are difficult to interpret as they could be related to other factors, like temperature (Polgár et al. 2019).

      Piloerection is a physical response outside a dog’s control akin to getting goosebumps. This reflexive response can be seen in a dog’s hackles, or erect hair. Hackles run from the base of the tail to the shoulders, and because raised hackles indicate arousal in general, piloerection should be evaluated in conjunction with ear, tail, mouth, and overall body posture to assess specifics of the aroused state.

      Tails are integral to communicative signaling. They can assume a range of heights, movements, and speeds, and even the side‐of‐wag offers meaningful information. Observing the tail‐base provides details as to whether the tail is being carried along the midline or is raised or tucked. Generally speaking, a high tail indicates excitement or arousal, and a high tail can be seen in a variety of approach‐oriented contexts ranging from greeting and playing to fighting and threatening; lowered tails suggest fear, submission, or appeasement/affiliation (Kiley‐Worthington 1976). To explore the value of tails within intraspecific communication, Leaver and Reimchen (2008) designed a study where dogs encountered a mechanical dog outfitted with tails of different lengths (long or short) that could move or remain still. Dogs were more likely to approach the mechanical dog when the tail was long and wagging as opposed to when it was long and still, suggesting that absent other communicative signals, dogs interpreted a wagging tail as “friendly.” On the other hand, a short tail, whether still or wagging, was approached similarly, suggesting that short (or docked) tails might be more difficult to view or interpret. Tail absence or surgical shortening affects communication (Bennett and Perini 2003).

Probably the most noticeable component of the tail relates to movement. A tail wagging fluidly and loosely from side to side (usually at the level of the midline) is most readily associated with greeting or excitement. This “happy” tail might be accompanied by jumping, licking, running in circles, or other behaviors of arousal. A tail wagging low and quickly indicates nervousness or timidity. High, fast wags indicate arousal, and they should be viewed with some caution. Arousal can take different forms, such as general excitement, interest in interacting, or even aggression. There are further individual variations in wags—circling, going more counter‐ than clockwise, banging—whose significance has not been studied (and should not be assumed). Tails can also lack movement and be held in a stiff, still position at all heights, which could either be the dog’s natural tail position or a postural display. Stillness is common in dog interactions: for example, play incorporates entire body pauses (including the tail) interspersed within fluid movements and play signals. Outside of play, a still tail should be evaluated along with the entire body to assess meaning.

      While often imperceptible to the naked human eye, wags can be performed asymmetrically—more to the right or left of midline—and offer insight into stimulus perception or emotional valence due to brain lateralization hypotheses (Siniscalchi et al. 2021). For example, dogs wagged more to the right side when encountering an owner (suggesting positive valence), while the sight of an unknown, unfriendly dog, prompted more left‐side wags (negative valence) (Quaranta et al. 2007). When