Drill Bros.

Baby Drill is a technique used by Baby Mario and Baby Luigi in Mario & Luigi: Partners in Time. The babies learn this technique shortly after they receive their Hammers in the Vim Factory. It is taught to them by the L33t Hamm3r Broz., and allows the toddlers to burrow underground - avoiding enemies and allowing them to slip under the tightest spaces. The babies cannot dig through hard materials (such as metal), and will receive a Bean if they surface on an 'X' marked spot.

The technique returns in Mario & Luigi: Bowser's Inside Story under the name of Drill Bros. It is usable by Mario and Luigi and serves a similar function to the last game, letting them traverse under tight areas and find Beans in the overworld, marked with again an 'X'.

Trivia

 * When the babies use Baby Drill when the bros. are inside Yoob, at the upper screen, he is seen blowing smoke from his nose.