Out Of Time - S1-E10
Continuity mistake: John is about to eat liver and potato with Emma before she storms out saying, "I don't like liver". While they are talking, the potato is facing Emma and Gwen. After Emma leaves, the liver faces Gwen and the spot where Emma was.
Answer: Several times during the episode, most notably at the beginning when the old grave is discovered, Tosh holds a devise that looks a great deal like the Sonic Screwdriver that she uses to determine the age of the skeleton. However, a search of Google images shows that it is not the same thing.
OneHappyHusky