The Adhesive Duck Deficiency - S3-E8
Character mistake: When Penny is telling Sheldon to sing "Soft Kitty" as a round, she (twice) tells him to come in after two bars. When he actually joins in, he comes in after one bar.
The Paintball Scattering - S12-E11
Other mistake: When Penny and Leonard are in the paintball shack, Leonard won't shoot Penny because they are too close and it would hurt. Penny doesn't believe him, but eventually, he shoots her in the chest, and she says in pain, "You're right, we're way too close." But Penny should already know what this feels like; she was shot in the chest from close range in a paintball shack by Sheldon in one of the earlier seasons when she shot his cushion with a paintball. So this feeling shouldn't surprise Penny in S12.
The Opening Night Excitation - S9-E11
Continuity mistake: When Professor Proton tries to stab himself with the lightsaber, he is originally holding Obi-Wan's lightsaber from The Phantom Menace. When the shot changes, he is then holding Anakin's lightsaber from Revenge of the Sith. When the shot changes again, it's back to Obi-Wan's lightsaber hilt.
