Para se certificar de que é realmente sangue, e (em alguns casos) identificar que tipo de sangue é / qualquer saliva de sangue informal
Como observado na entrada da TV Tropos, O teste de ketchup é onde:
a character touches a blood stain with his fingers, usually in order to make sure that it actually is blood. Sometimes, it turns out to be ketchup or strawberry jam (something that's red, goopy and fake), especially if another character has been doing a Chicken Little impersonation over the supposed bloodstain.
Being a vampire or a cyborg may also help for analysing the type of blood. In Real Life, it's possible that some animals (bloodhounds, brown bears, tyrannosaurs, larger sharks) may have a sufficiently powerful sense of smell, this (or simply sniffing the blood) might actually allow them to determine the species or even the individual victim involved.
See also Sniff Sniff Nom, Fingertip Drug Analysis.
Existem muitos exemplos nos links acima de charcters que usam o teste de sabor como uma maneira de aprofundar sua compreensão de uma situação.
Também pode ser que tocar o sangue permita que o personagem identifique qualquer coagulação, o que pode ajudar a identificar há quanto tempo o sangue entrou em contato com a superfície e de que parte do corpo:
Blood is in a liquid state when inside the body, and when it exits the body, it does so as a liquid. But as anyone who has had a cut or a scrape knows, it doesn’t remain a liquid for long. Except for people with hemophilia, blood will begin to clot within a few minutes, forming a dark, shiny gel-like substance that grows more solid as time progresses.
The presence of blood clots in bloodstains can indicate that the attack was prolonged, or that the victim was bleeding for some time after the injury occurred.