what should a guy do when his date starting to talk about marriage plans on the third date?

[an Imaginary cat owner]

1-fake a heart attack
2-go to the bathroom and jump from the window
3-play along and change your number
4- ?
Starts to talk*

[LaserTek]

Definitely not the third if you're not serious about that yet. Maybe you could just keep quite and let her talk. Just DO NOT give her false promises. If you dare, good luck with the outcome. That's like calling for trouble! You know girls, we easily give meanings.