Several bacterial pathogens, including Vibrio cholerae, use toxins containing actin crosslinking domains (ACDs) to interfere with the ability of the host cell to polymerize actin. The toxicity of ACD-containing toxins is thought to arise via sequestration of bulk amounts of actin as non-functional oligomers, which ultimately results in failure of the cytoskeleton. Now, a new study shows that ACD-containing toxins also work by converting actin into a toxic oligomer that interferes with formins, which are a family of proteins involved in the nucleation and elongation of actin filaments. The authors show that ACD-modified actin filaments bind with high affinity to formins and inhibit their activity. These data suggest that ACD-containing toxins act not only by sequestering actin but also by 'poisoning' proteins involved in actin polymerization.