When the Warlock Gavin kills one of the effects shown is the eyes drained of color, this is confirmed by Andy (at around 46 mins), however when the corpse of the first victim is found (at around 13 mins) the eyes were shown as normal.
While at the manor after Tanya is attacked, Phoebe supposedly does first aid on the burn mark on Tanya's forehead. Phoebe very obviously does it around the mark so as not to mess up the make up on her forehead to make it look like she was burned.
When the warlock asks Prue about Tanya she says she doesn't remember. This was obviously a lie, and Prue was under the truth spell. She shouldn't have been able to lie.
After trying to reach Prue at Buckland's, Piper tells Phoebe 'it's after 5, it's going straight to voicemail.' But when she was on the phone, it was ringing not going straight to voicemail.
Phoebe tells Tanya that Gavin is a demon, but he is a warlock.
Phoebe is able to prevent Prue from revealing her identity as a witch to Rex by interrupting Prue and changing the word witch to "winner". This, however, is a lie, and would not be ale to occur under the 24 hour truth spell.