by Merry Youle — Bac­te­rio­phages are ex­pert killers, hav­ing been de­liv­er­ing death to bac­te­ria for sev­eral bil­lion years. We are not the first or­gan­isms to rec­og­nize their skill. Bac­te­ria them­selves have bor­rowed the tail of a phage and fash­ioned from it a tar­geted bac­te­r­ial killer for their own use. We first be­came aware of this in 1925 when An­dré Gra­tia ob­served...