from collections import defaultdict

def detect_periodic_connections(connections):
    pair_counts = defaultdict(int)

    for c in connections:
        key = (c["src"], c["dst"])
        pair_counts[key] += 1

    findings = []
    for (src, dst), count in pair_counts.items():
        if count >= 50:
            findings.append({
                "behavior": "PERIODIC_COMMUNICATION",
                "src": src,
                "dst": dst,
                "count": count
            })

    return findings
