Near the end of Men in Black, Kay kills the bug from the inside.
But when Jay and Kay thinks it's over, another bug suddenly appears, and almost eats Jay.
What is that 2nd bug doing there? How and when did it come to Earth? Were both bugs working together to find the galaxy? Was it a rival of the first bug, and wanted to steal the galaxy? Or maybe it didn't want the galaxy at all, he was just there to use the flying saucer to escape from Earth before destroyed?
It's the same bug. Kay didn't kill it, he just wounded it mortally.
Bug gets blown in half by Kay
Front half sneaks up behind Jay and Kay
This is backed up in the script
As they argue, behind them, unseen, THE FRONT HALF OF THE BUG RAISES ITSELF UP on its forearms, eyes gleaming with hate, jaws dripping -- ready to lower itself onto Kay and Jay.
JAY: After I got the shit beat out of me!
The film's Official Novelisation is a little more detailed, but basically confirms what's in the script.
Jay sensed rather than saw what happened next. Felt a sense of sudden dread envelop him. Spun—
—saw the top half of the bug, levered up on its arms, mouth open, about to fall on them.
"Oh, shit!"
Kerb dragged his upper half toward the humans. It was going to strain his regeneration capabilities to their utmost to survive this one. Maybe he wouldn't make it. Truth was, he didn't know any of his species who'd lost their whole bottom half and come back, but he was tough. There was always a first time.
Whatever, he had to kill these damned humans. At the very least, if he was going to cross over the Bridge to the Other Side, he was not going without the company of those who'd sent him there.
He lifted himself, opened his mouth. Now—!
Jay screamed, something wordless, and prepared to die—
Boom! The bug's head shattered, blew apart. Bits of chitin and brain and circulating fluid splashed and pattered all over Jay and Kay, organic shrapnel.
