The paper explores the puzzle of why cosmological data, particularly from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI), prefers negative neutrino masses. The authors investigate which data is most responsible for this preference and whether it is related to other cosmological anomalies. They conclude that the preference for negative neutrino masses is primarily due to larger-than-expected lensing of the CMB in both two- and four-point lensing statistics. This preference is robust to changes in the likelihoods of BAO and CMB optical depth analyses. The excess clustering is not easily explained by changes in the expansion history and is distinct from the preference for dynamical dark energy in DESI BAO data. The authors also discuss how future data, including Planck CMB with mock DESI 5-year data, may impact these results. They conclude that the negative neutrino mass preference is likely to persist even with more cosmological data in the near future.The paper explores the puzzle of why cosmological data, particularly from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI), prefers negative neutrino masses. The authors investigate which data is most responsible for this preference and whether it is related to other cosmological anomalies. They conclude that the preference for negative neutrino masses is primarily due to larger-than-expected lensing of the CMB in both two- and four-point lensing statistics. This preference is robust to changes in the likelihoods of BAO and CMB optical depth analyses. The excess clustering is not easily explained by changes in the expansion history and is distinct from the preference for dynamical dark energy in DESI BAO data. The authors also discuss how future data, including Planck CMB with mock DESI 5-year data, may impact these results. They conclude that the negative neutrino mass preference is likely to persist even with more cosmological data in the near future.