Twiba wearing a hard hat, while creepily staring at you, an implication that she may be inhaling your soul.
Hard hats are strange helmet things and may be weapons that the Dig-Its wear on their heads most of the time. Most of the time, though, due to the fact that Twiba, the leader, is not often seen wearing one, though. But the most predominant of the population of Dig-Its has been reported to often be seen wearing a hard hat. Every known Dig-It has been reported to possess one though, even if they do not wear it on a daily basis.
Hard hats were first invented by some random Dig-It known as Twteit Hardhat in the year of 311 years ABB, when thinking of inventing a sort of headgear intended to protect a Dig-It's head from injury during the process of digging it, and decided to name it after himself due to his gigantic ego. It is suspected that wild hot lasers come out of the headlight present on a typical Dig-It's hard hat, which is why they are suspected to likely be weapons.
Although hard hats are a well known headgear created and wore by the Dig-Its themselves specifically, Bob the Builder wears one for some reason. This brings up the suggestion and may prove that the Dig-Its once tried to indoctrinate him into their cult by gluing a hard hat on his head with their nasty Dig-It superglue.