Episode 4 (S04E04)

Granville encourages Gastric to express his artistic side in a local art competition, but he throws himself into self-expression more enthusiastically than anyone could have predicted. Meanwhile, Granville has bought a large collection of mystery tins. Unfortunately, Leroy and Granville are still none the wiser on the contents after they've opened one. Now they face the ultimate challenge – how can you sell something when you have absolutely no idea what it is? (BBC)