Why can't you hear a pterodactyl go to the toilet?
Because the P is silent.
Because the P is silent.
Nice!
I like this because it turns it into an anti-joke. Plus it's good to have a backup punchline if they get it right.
I just told this to my girlfriend and she answered it correctly, following with "dude, that joke is so old my grandfather used to tell us that in the bath." so like this joke is 300 yrs old.
This joke was in a book I was reading to the boy last night. I got him to learn it so he could tell it to his teacher today.