Комментарии: PAT *č́č́a- (assimilated < *š(ǝ)č́a-); PAK *č́xǝ-; Ub. sǝ-šʷač́á-n. Shagirov (2,149) justly criticizes Klimov (1967, 304) for comparing PAT *č́č́a- with PAK *š́ǝš́ǝ- 'to neigh', and follows Abdokov (1973, 24) in comparing PAT *č́č́a- and PAK *č́xǝ-; he also adds the Ubykh form, but only its second part (-č́a) - see Shagirov 2, 149.
Since PAK *č́ = Ub. č́ and PAK *x = Ub. šʷ, it seems very probable to compare the words in whole (assuming a metathesis in one of the subgroups). The PAT form *č́č́a can be easily explained as a result of assimilation < *šǝč́a (where *š < *ʎ́ʷ and *č́ < *č́). Therefore the commonly accepted comparison of Abkh. -č́č́a- with PK *cc- 'to laugh' (Charaya 1912, 48, Shagirov ibid etc.) seems rather superficial. If PWC *ʎ́ʷV-č́V- (*č́V-ʎ́ʷV) is a compound verb, only its component *č́V can be compared with Kartvelian (we should add that both forms are probably onomatopeic in origin); the component *ʎ́ʷV is certainly related to EC forms meaning 'to laugh'.