Reference for Eruvin 40:3

כל היכא דקא נקיט מנא ולא נקיט לה לא תיבעי לך דבעי ראשה ורובה מלגיו כי תבעי לך היכא דנקיט מנא ונקיט לה מאי

and does not hold the animal there can be no question that it is necessary for its head and the greater part of its body to b within [the private domain].<span class="x" onmousemove="('comment',' Since otherwise it might pull its head sideways or backwards and thus drag the vessel with the man into the public domain.');">⁴</span> The question only arises where he holds the vessel and also the animal.

Jastrow

Jastrow