The shift is rather suspended. The lexeme paḥad is not attested as an euphemism for testicles in the Bible (> ˀäšäk אשך). The passage about hippopotamus in Job 40:17 yaḥpōṣ zәnāḇō ḵәmō ˀāräz gīḏē paḥaḏāu yәsōrāgū is thus problematic. The form paḥaḏāu is considered to mean 'testicles' here becuase of the adjacent words zәnāḇō (see the Hbr. realisation tail->penis) and yaḥpōṣ (verb ḥāpēṣ חפץ 'to desire, to take pleasure in'). The cognate in Arb.فَخِذٌ  faḫiḏ- 'thigh' as an euphemism is not attested as well, and has no sexual connotations. In Aramaic there is also no such a thing (vs. Jastrow's etymology). Hapax in Job. -d is probably due to the Arm. origin of the word (*פחז > פחד). 

The idea of bibleistic scholars is rendered as follows: "The testicles of the hippopotamus are however internal, and so could hardly form a tpoic for the poet's description."

Cf. also Arb. أُنْثَيَانِ dual. 'testicles' (lit. 'two women'). The idea behind is that testicles as the witnesses of copulation (for more see Kogan, Bulakh, 2013. The Arabic-Ethiopic Glossary by al-Malik al-Afḍal).