Computers have also been used to simulate and estimate the potential damage that a product or chemical can cause, and human tissues and cells have been used to examine the effects of harmful substances. In another method, in vitro testing, cellular tests are done inside a test tube. All of these tests have been proven to be useful and reliable alternatives to testing products on live animals. Therefore, because effective means of product toxicity testing are available without the use of live animal specimens, testing potentially deadly substances on animals is unnecessary.