The primary mode of transmission is via deep bite wounds, in which the infected cat's saliva enters the other cat's tissues. FIV may also be transmitted from pregnant females to their offspring in utero; however, this vertical transmission is considered to be relatively rare, based on the small number of FIV-infected kittens and adolescents.[1][2] This differs from FeLV, which may be spread by more casual, non-aggressive contact, such as mutual grooming and sharing of food bowls.[citation needed]