From The AP:
A spacewalking astronaut accidentally let go of her tool bag Tuesday after a grease gun inside it exploded, and helplessly watched as the tote and everything inside floated away.
It was one of the largest items ever to be lost by a spacewalker, and occurred during an unprecedented attempt to clean and lube a gummed-up joint at the international space station. Heidemarie Stefanyshyn-Piper was just starting to work on the joint when the mishap occurred.
She said her grease gun exploded, getting the dark gray stuff all over a camera and her gloves. While she was wiping everything off, the white, backpack-size bag slipped out of her grip, and she lost all her tools.
"Oh, great," she mumbled.
Earlier, the spacewalkers spotted a screw floating by, but were too far away to catch it. "I have no idea where it came from," Stefanyshyn-Piper told Mission Control.
NASA was not sure how the bag got loose; it should have been tethered to a larger equipment bag. Another unknown: why the grease gun discharged.