L~R:

perl -e "use warnings; print qq{yeah$/} if 'p2p' == 'f2b'; print 'p2p'
+ + 0"
Argument "f2b" isn't numeric in numeric eq (==) at -e line 1.
Argument "p2p" isn't numeric in numeric eq (==) at -e line 1.
Argument "p2p" isn't numeric in addition (+) at -e line 1.
yeah
0
[download]

Non-numeric arguments are treated as 0 in numeric operations. == is a numeric comparision operator, its string equivalent being eq.
I remember reading somewhere (maybe the camel or llama book) that numbers in string representations may have a newline character after them, which would explain why you don't need to chomp. I couldn't find the passage, though.
Cheers,
CombatSquirrel.

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Entropy is the tendency of everything going to hell.