What is the principal image in bi-shiqq wa-taḥtī shiqquhā?

Imruʾ al-Qays: Dialogue in ʿUnayzah’s Litter, Boasting, and an Oath (Verses 13–18)

• One half of the body turns to the child while the other remains by the speaker
• Two separate camels walking together
• A sand dune collapsing
• Two water vessels being joined