The model of the speech circuit proposed by Ferdinand de Saussure in "Course in General Linguistics" (1966 [1916]). A conversation is an exchange of vocalized mental signs. The drawing uses the oak clipart by rg1024 http://www.openclipart.org/detail/colored-oak-tree-by-rg1024
Cordless and corded power drills with bit set. The corded drill in this image is known as a hammer drill while the cordless drill is your standard battery powered drill. This vector illustration is 20+ years old but the drills still look like any drills you'd find on a store shelf.