thing['severity'] = thing['severity'].str.lower().replace('unknown', np.nan)
thing['trigger'] = thing['trigger'].str.lower().replace('unknown', np.nan)
thing['landslide_type'] = thing['landslide_type'].str.lower().replace('unknown', np.nan)
thing['country'] = thing['country'].str.lower().replace('unitedâ\xa0states', 'united states')
thing.head()