Reference for Keritot 43:2

דם שעל גבי ככר גוררו ואוכלו של בין השינים מוצץ ובולע ואינו חושש

whilst in the instance of Rab it had not been separated; as it has been taught: The blood found on a loaf of bread must be scraped away and the loaf may be eaten; that between the teeth may be sucked and swallowed without hesitation.

Jastrow