Grange Hill : Season 1 Episode 5

Trisha is helping Rankin, an elderly biology teacher, with various odd-jobs in the lab during lunch breaks. Judy comes to see her in the lab one day when Rankin is away. Trisha decides to show off to Judy by taking a hamster out of its cage. The hamster escapes. Another teacher, Miss Clarke, appears. Although she does not notice the absent hamster she gives Trisha a detention for wearing earrings. It seems the hamster has escaped outdoors. Judy runs to a petshop in an effort to buy a replacement hamster. It costs £1.25. Judy makes it back to the biology lab just before Rankin arrives. He notices the difference immediately. The original hamster comes back also and Rankin says that the replacement was both the wrong colour AND the wrong sex. Rankin lets the girls off with no punishment.