On the one hand, R. gnavus could just be a bystander as mucus-degrading bacteria, profiting from mucus changes in inflammatory conditions, such as increased mucus thickness and upregulation of Muc2 secretion, which have both been described for Crohn’s disease (Smirnova et al., 2001; Strugala et al., 2008; Crost et al., 2013). The gene discussed is MUC2; the disease is Crohn disease.