Table 1. Criteria used for identifying intentional production of communicative signals, as outlined in the study of great ape gestures [19]–[36].

Criteria	Explanation
Social use	The signal is directed at a recipient. This can be assessed at various levels:
	1. Presence/absence audience effect: the signal is only produced in the presence of a recipient.
	2. Composition of audience: the signal is only produced in the presence of certain recipients (e.g., kin, dominants, friends)
	3. Behaviour of audience: signal production is contingent on the behaviour of the recipient
Sensitivity to attentionalstate of recipient*	Visual signals are only produced in the field of view of recipients. If signaller does not have a recipient’s visual attention, tactile or auditory signals should be produced. This can also be considered a level (3) audience effect.
Manipulation of attentional state of recipient*	Before a visual signal is produced, attention-getting behaviours are directed towards a recipient who is not visually attending to the signaller.
Audience checking andgaze alternation	Signaller monitors the audience and visually orients towards the recipient before producing a signal. If a third entity is involved, gaze alternation may occur between recipients and this entity.
Persistence or elaboration	Goal-directed signalling shown by repetition of the same signal (persistence), or production of different signals (elaboration) until the desired goal is met.

^*indicates applicable only to visual signals and therefore not relevant for vocal production.