Accidentally Saying Chinese Swear Words So I saw a video on youtube about a guys experience in china. He said that people can often accidentally say swear words if they say the tones wrong. Like the word "ma"

It can heard as mother but 'ma' can also be heard as horse in a foul way. Is there any pinyin/character combinations that I should be careful to write or say wrong/all together? 

And for swear words, do they use the same character they use for the word or is it written differently? Also maybe describe a experience that you accidentally said a swear word in Chinese.
A story tells of an ethnic minority student who simply wanted to borrow a pen from a female comrade. Ethnic minorites in China are often as tone deaf as Westerners, and when the guy wanted to borrow a pen (借你的笔 / jie4 ni3 de bi3), it became 借你的屄 (jie4 ni3 de bi1), and the female student got all red in her face pondering the proposal of lending her cunt to that fellow...

The words and tones to look out for are the following:


cào (肏，操), which means fuck (often heard as 我操, i fuck, simply meaning fuck)
bī (屄，逼), which means cunt (often rendered as 傻屄 or 傻逼 (sha3bi1), meaning stupid cunt)


gàn is not problematic in China, only in Taiwan.

mā de (妈的) is a very mild swear sentence in China.