To re-engineer the mice, scientists led by Jeffrey Martens programmed a cold virus with normal IFT88 genes and infected the animals with it. The virus did what viruses do, invading the mouse's cells and replicating. This inserted the new DNA sequence into the mice, which in turn caused the cilia to re-grow from the ends of the olfactory neuron. This had a notable effect on the appetites of the mice -- after just two weeks, the mice increased their body weight by 60 percent. The scientists put some smelly substances in front of the animals and noticed their neurons were firing as they should.