(Current Biology 19, 881–890; June 9, 2009) In this paper, we miscalculated absolute weight of an odorant based on a dilution factor. Through the entire manuscript, the dilution factor is correct, but the converted absolute amounts were 2-fold smaller than the correct values. On page 887, line 26 in the left column, 3 ml of 10 diluted solution should correspond to 30 pg, not 0.3 pg. Accordingly, in the last paragraph of the Results, the 0.3 pg–3 ng range should be 30 pg–300 ng. The fourth sentence of the Summary should read ‘‘a threshold of 30 pg from 20 cm distance.’’ In Figure 1C and the corresponding text, the odorant amounts should range from 30 ng to 30 mg. Although these errors do not affect our conclusions, the authors regret the miscalculation and apologize for any inconvenience that they might have caused.