I have a funny story related to the third tone...

I was out with a few friends and one asked me 你春节有什么打算 (ni3 chun1jie2 you3 shen2me da3suan4 = what plans do you have for Spring Festival?). My friend, being a Chinese native speaker, pronounced 打 as a low tone and not a falling-rising. But because I was still under the misimpression that "tone 3 = falling-rising" I misheard 打 as a fourth tone! Therefore 打算 (da3suan4 = plan) became 大蒜 (da4suan4 = garlic). Her question sounded totally bizarre to me: 你春节有什么大蒜？(What garlic do you have for Spring Festival?).

I actually answered this way: "What!! Chinese people eat a special kind of "New Year Garlic" for Chinese New Year?!"...

Everyone was extremely confused by this strange conversation, not just me...

@Phil:I believe native speakers do indeed drop back down for second-tone pairs. However the second vowel won't necessarily rise as high as the first. You can see the pitch contour of 流行 (liu2xing2) perfectly using the linguistic analysis software Praat in this interesting article

http://www.sinosplice.com/life/archives/2008/01/21/seeing-the-tones-of-mandarin-chinese-with-praat

Note, also, the third-tone pitch contour in 狡猾 (jiao3hua2)...the third tone drops and never rises.

I'm only just barely starting to figure out how Praat can be used in language learning, but it seems to have a lot of practical potential.

(PS: thanks for your correction, Ruby. Of course, third tone is not the only tone that changes in connected speech, I was incorrect to say so)

I agree that the best way to get used to the "falling low" third tone is to learn it in common words or collocations, such as 可能 （ke3neng2)，打电话 (da3dian4hua4)，给他 (gei3ta1). All of these third tones are low tones, not a single one is falling-rising. In fact, I find falling-rising third tones the exception rather than the rule. Here are some examples to show my point:

给我 (gei3wo3)，给你 (gei3ni3)，给她/他 (gei3ta1)

Notice how in 给他 (gei3ta1) the third tone is low, whereas in 给我 and 给你 (gei3wo3/gei3ni3) it's rising! In other words, 给 is never falling-rising when followed by a pronoun!

Whenever 买 is followed by tone 1, 2 or 4 it's not really a falling-rising, it's a low tone! And when it's followed by a tone 3, it's not falling-rising either: it's simply rising! When is 买 falling-rising? Never, when followed by a noun!

So when exactly is third tone falling-rising? Not very often! Only when it's either:

A. The last syllable in a word,

B. Stressed, or

C. In isolation.

In other words there are three possible pronunciations of the third tone (low, rising, falling-rising), whereas the other tones have just one! How horrible is that!!!

Can you give some examples of confusing second tone words for your students, ruby? I'm quite curious!

完全同意！

I totally agree. I think the 2nd tone is hardest both to produce and to hear. After studying awhile (years), other tones "fall into place," but the 2nd tone is forever a "thorn in my side"!!! There are some tricks, I think, and that is mainly to work on it in combination with other tones, which is the best way to work on tones, anyway, in my humble opinion...