Goes Upstream

Ralphie wants to catch salmon to serve at the annual school picnic, but he can't find any at his favourite fishing spot. Where could all the salmon have gone? The kids are soon "Frizzled" inside a salmon bus that has an uncontrollable urge to head upriver. "Wait!" Ralphie cries. "We'll be late for the picnic!" But the salmon bus won't stop. Using its sense of taste and smell, it swims the long journey to a shallow freshwater stream miles away. Why has the bus, which thinks it's a salmon ,gone to all this trouble?