Learn Spanish (Latin America): Se me cayó la fritura por la grasa. - I dropped the fried snack because of the grease.

Se me cayó uses the accidental se construction, which shifts the blame away from the speaker. Literally, it translates to 'the fried snack fell from me.' While dejé caer means 'I let it fall' (which can sound intentional), se me cayó emphasizes that it was a complete accident.

How would I use the adjective puro from this lesson to say I dropped it because it was 'pure grease'?

You would change the end of the sentence to por pura grasa. In Latin America, placing puro (or pura) right before a noun emphasizes exclusivity or excess, meaning the snack was so slippery it felt like 'nothing but grease.' Notice that you drop the article la when doing this.

If I dropped two fried snacks, how would this sentence change?

It would become Se me cayeron las frituras por la grasa. In the accidental se construction, the thing that falls is actually the grammatical subject of the sentence. Because las frituras is plural, the verb caer must also be in the plural form (cayeron).

Why do we use por here instead of para to say 'because of'?

Por is used here because it introduces the cause or reason for the action. The grease caused the snack to slip. If you used para, it would imply a goal or purpose, which doesn't make sense when explaining why something accidentally fell.