The door to the right of the drop into the trash compactor where Meg is fought.
The door on the left-hand wall directly beside the bottom of the stairs leading into the Hall of Wonders from the Claptrap repair shop.
The door closest to the shops opposite the entrance to Harren's Lockup, where Professor Nakayama is found.
Corporal Bob shoots at Vault Hunters while closing to melee range, whereupon he attacks with his fists. While running toward the Vault Hunters, he can also occasionally drop a unique Lost Legion Wormhole Generator named Lost Legion Flame Turret, which acts as a normal Wormhole Generator (pulling Vault Hunters closer to it) and as an incendiary grenade (spinning around and firing quick bursts of flame).
The "Talk to Jack" objective in the story mission Science and Violence must be completed first before Corporal Bob can actually be found.