'...at the end of the meal you should leave a little on the plate to demonstrate the generosity of the host.'
Death is an unwritten rule to not talk about in China, and learned it the hardway when I told a Chinese friend who didn't take my calls for 6 hours "I thought you had died" in our common younger and cheek way.
Sì = Four
Sǐ = Die
Because of the taboo over death and it shall not be suggested, four is a number Chinese will avoid as it is easy to miss pronounce it and sound like the word for "die".
Most will never order 4 dishes, it is 3 or 5, even if 5th is not touched, but never 4.
Prices are rounded up or down around 4, I know one contract I negotiated we had to change the currency for us to get the best price as they wanted $5 for something they had calculated to being $4.
Buildings often miss or skip having a 4th floor.
You can get SIM cards containing a lot of 4's in the number for half the cost of credit that comes with them as most Chinese will not touch them and a phone number containing one 4 is a hard sell.