Kiddushin 81 - Don't Scoff at Sinners

Rabbi Akiva was accustomed to scoff at sinners, because he felt that it is a simple matter to overcome the temptations of the Evil Inclination, if only one desires to do so.

One day Satan appeared to him disguised as a woman, perched atop a palm tree. Rabbi Akiva began to climb to meet "her". When he reached the middle, Satan released him from his grip and said: "Had they not proclaimed in Heaven - 'Be cautious of Rabbi Akiva and his Torah,' - I would have made your life worthless."

Students of Shmuel were careful not to be alone with an animal, but this is normally not required.