Walt begins his first chemotherapy session while resuming his partnership with Jesse. During a cooking session, Jesse notices radiation therapy marks on Walt's chest and deduces he has lung cancer. Hank traces the gas mask found in the desert to Walt's high school chemistry lab and arrests the school janitor Hugo, who has a criminal record and marijuana in his car. Walt shaves his head when his hair begins falling out from treatment. Their first batch yields only $2,600, prompting Walt to demand increased production. Jesse's friend Skinny Pete introduces him to Tuco Salamanca, the violent drug lord who replaced Krazy-8 as the area's main distributor. When Jesse demands upfront payment for their meth, Tuco savagely beats him and steals the product without paying. Walt confronts Tuco alone at his headquarters, detonating an explosive device he created using fulminated mercury. The explosion destroys part of Tuco's office and demonstrates Walt's dangerous capabilities. Impressed by Walt's boldness and the quality of his product, Tuco agrees to pay for the stolen meth and establish a regular business relationship with Walt and Jesse.