A flea is a type of insect that feeds on the blood of mammals. A tick is a type of parasitic bug that also feeds on blood. Lice is the plural of louse, a type of parasitic insect that feed on blood. Lice kind of sounds like "lies". The word "lice" was used to replace "lies" as a joke because the joke is talking about insects that feed on blood. This joke is playing on the word lice.
Don ' t believe what you hear about fleas and ticks - - it ' s all lice .