In Parshas Chukas it says they took out the Parah Adumah to Schecht(ritually slaughter) the Targum Yonsan says and they checked it for Treifos (illness or wounds that would render the animal un-kosher).There is a problem with this as it was not possible to check it for Treifos you had to burn it completely?So how did this checking happen?
1)The question is answered by one of my favorite Medrashic answers brought by a Tosfos in Shabbos (Daf Chof Beis Amud Beis ד"ה וכי לאורה) which Suggests pre-knowledge of modern technology of Chazal. It is said that The Annanie Hakovod(Clouds of Glory)provided an X-ray of the insides of the cow and hence they where able to Check for Treifos. (Har Tzvi on Parshas Chukas)
2)Another answered provided by Rabenu Bachaya in Parshas Tzav is that Cohanim had indicators of Treifos externally and as such where able to tell of any internal Treifos, a lot less fun but a way more practical answer.