Short Sales on 2nd mortgage

[Martin Sterling]

Question about podcast 106 with Mike Sumsky

If borrower is behind and the property is worth 100k.
They owe 75k on 1st Mortgage and 35k on 2nd Mortgage, the interviewee on the podcast said he will get the 2nd Mortgage for $1500 because lender won't get anything in a auction. Couldn't the 2nd just foreclose? Couldn't they bid up the price in the auction to cover their debt? Why would they accept that?

The interviewee also said they short sale the 2nd mortgage and took over the 1st Mortgage subject to?

How do you short sale a 2nd Mortgage?

What is a buyer buying and why?

Thanks in advance