This is an odd, reasonably pointless expression that returns 7 in any R5RS-compliant Scheme implementation:

(let ((x (lambda (z) z)) (y 7))
    (let ((x (lambda () x))) y))

This is an infinite loop in any R5RS-compliant Scheme implementation:

(let let ((x (lambda (z) z)) (y 7))
    (let ((x (lambda () x))) y))

Gotta love overloaded syntax.