Anas ibn Mālik (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "When Allah fashioned Adam in Paradise, He left him (in the form He created him) as long as He desired to leave him (i.e. for a certain period of time). Satan started to go round Adam looking at him. Once he saw that Adam had a hollow body, he realized that he was a weak creature."
When Allah created Adam in Paradise and shaped his image, He left him for some time before blowing life into him. So Satan started to walk around him in circles and look closely at him to find out what this creation was. When he saw that Adam was hollow on the inside, he knew that it was a weak creature that does not have the ability to ward off the whispering of Satan, or he knew that that creature would commit a sin motivated by his insides (since he sinned by eating from the forbidden tree), or he knew that creatures that are hollow on the inside are weak. Some people considered the words: "in Paradise" to be problematic, given the narrations that say that Allah created Adam from different parts of the earth. The answer that was given to those people is that it is possible that Adam was left like that until he went through several stages and his image was ready for the breathing of life into it, then it was carried to Paradise where life was blown into him there.