He does this thing where he tries to intimidate people by unexpectedly pulling them during a handshake. She was ready for him, to the point that he had to add in another hand to avoid her pulling him instead.

https://youtu.be/FZOJ0kZeZDE?si=5sH2rymlnl5a_Lsm

Watch Biden’s face following the handshake (it’s right at the beginning of this link).