Comments: PAT *pǝśǝ-ʕa- (cf. also Bz. a-pśā́,a-pśā́-ṭʷ 'bird', Abaz. pssʕa-č̣ʷǝ id.); -ʕa is obviously a suffix. PAK *bzǝ-wǝ́ (where -wǝ is an archaic diminutive suffix).
Reconstruction of PAT *ś (and, therefore, PWC *š) is based on Abkh. Bzyb. evidence quoted in Marr's dictionary; since Bghazhba has not included the word in his book, it may well be Marr's misspelling - in that case we must reconstruct simply PAT *pǝsǝ-ʕa- and PWC *bǝsA.