As romulus stated, sometimes word order can be rather flexible, particularly when the writing is meant to be poetic or artistic. For instance I could take a rather standard sentence "I ran towards Jimmy." (Standard English SVO) and change it to "Towards Jimmy I ran" (OSV), and you'll even run across the odd Star Wars, Yoda reference and get a sentence structured as "Ran towards Jimmy I did." However, in the sentences I see they seem to be article/grammar mistakes. "In" generally refers to a location, in this case it's being used with an action which is incorrect. It makes more sense without the in. The second also has a grammatical error. The 'it' is unneeded because the topic has already been stated as well as its placement would be incorrect in this type of statement. The writer probably used a sentence type such as "There is a tree behind it." as a model for the structure, but because of the changes in the sentence it isn't a very good model.

Hi, michelle English is more of a get-right-to-the-point language. That means in a sentence, the parts seen as more important will come first and the parts seen as less important will go to the end. However, it is not the case when the sentence is somewhat a long one. When a sentence is long, new messages will bump out the old ones in our short-term memory, which kind of makes the latest info both the important piece and the focus of our attention since we can't quite recall what exactly went before it. Writing stylists will then take advantage of this defect of ours and reverse the word order a bit when they want the audiences' attention falls naturally on the end of a sentence. In the sentence "Spiders are busy for at least half the year in killing insects", the writer reversed the how (in killing insects) and the when (for at least half the year) because he/she wanted us to pay more attention to the how. In the sentence "The puma left behind it a trail of paw prints", the writer wanted us to pay more attention to the what (a trail of paw prints) instead of the where (behind it). Or rather, you can say this is actually a suspense-causing technique, where the secret will not be revealed until the end. Another example of this suspense-causing technique can be heard at a ceremony, where you will more often hear the emcee say "I'm proud to present to you (name of someone)", not the other way around (to present (name of someone) to you), because it is the next person on stage that is more important, not the audiences (you). Hope this helps and 新年快樂.

if you are writing it yourself, you can use the sentence pattern that you prefer. however, if you are writing a paragraph, making use of different sentence patterns prevents the paragraph from looking or sounding monotonuos like it was written and spoken by a robot. the mix of sentence patterns can also make the flow of the paragraph better.

English syntax is indeed flexible! In your above example, they're both grammatically correct. It's just that english speakers tend to 're-construct' the sentence structure to somehow boost the mood of the issue / matter (i.e. S-V-O or S-O-V pattern). zaijian!

I would take out the 'in'. Spiders are busy killing insects for at least half the year. In your 2nd example I would say, The puma left a trail of paw prints behind. the 'it' isn't needed