Bilbo sees the ring. In a moment he is possessed. He lurches forward and he transforms.
The eyes widen and become Gollum like. Bilbo is taken again by his 'prescious.'
Bilbo's fingers become pointed and extended. The fingers are almost like blades.
This takes us back to the Nazgul with their possesing, grabbing and searching fingers.
Bilbo recoils and suffers despair. The moment is one of regret and a lingering despair. Bilbo cannot be happy anywhere near the ring. Sight of the ring has obsessed him again and his usual distractions lose their pull for him. He is lost for a while.
The comforting hand of Frodo. Here we are reminded of the wider hand symbolism of Fellowship. Pointed, extended fingers are of the ego whilst open, connected hands are a symbol of fellowship. The fact that Bilbo connects to Frodo signals his redemption. The moment of possession was a passing shadow. The softer, more 'elf-like' Bilbo we find in Rivendell has returned.